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3  1918 

A  Study  of  the  Changes  in  Skins  During 
Their  Conversion  into  Leather 


A  thesis  submitted  in  partial  fulfillment  of  the  requirements  for  the 
Degree  of  Doctor  of  Philosophy  in  the  University  of  Michigan 


By 


Anton  Augustus  Schlichte 


Reprinted  from 

The  Journal  of  the  American  Leather  Chemists  Association 
December-November,  1915 


Copyright.  1915 


Meinen  lieben  Eltern  in 
Dankbarkeit  gewidmet 


326046 


CONTENTS. 


ACKNOWLEDGEMENT    3 

INTRODUCTION    3 

STUDY  OF  MICROSCOPIC  CHANGES  IN  HIDES  DURING  THEIR  CONVERSION 

INTO  LEATHER  6 

Review  of  Literature   6 

Experimental  Work  on  Technique  of  Imbedding  and  Cutting  Tissue  7 

(a)  Paraffine   Methods    7 

(b)  Celloidin  Methods    9 

(c)  Freezing   Method    10 

Study  of  Changes  in  Structure  during  Tanning 12 

STUDY  OF  CHANGES  IN  VOLUME  AND  WEIGHT  OF  CALFSKINS  DURING  THE 

LIMING  PROCESS  14 

Apparatus    15 

Experimental  Work  on  Calfskins 17 

Attempts  to  Remedy  Thinness  of  Flank 34 

Results    39 

STUDY  OF  DEPUTATION  IN  STERILE  LIMES 42 

Review   of   Literature 42 

Experimental  Work   43 

(a)   The   Sterilization  of  Skins 46 

(fr)   Laboratory  Tests  on  Depilation 48 

(c)   Depilation,  and  Subsequent?  T?annage 56 

CONCLUSION *,,  * V. .'«.  .*".  .'.'.-.<! 60 

BIBLIOGRAPHY    .  .*  .  ?  /.  .• ,: ;  .<;.*: * ;.:...;  .,',. ...  i 62 


ACKNOWLEDGEMENT. 

The  generosity  of  Mr.  Carl  E.  Schmidt  in  establishing  a  fel- 
lowship in  tanning  at  the  University  of  Michigan,  has  enabled 
the  author  to  pursue  for  3  years,  the  studies  outlined  in  this 
thesis.  Mr.  Schmidt  has,  moreover,  given  freely  of  his  time  and 
experience  and  it  is  a  pleasure  at  this  time  to  express  apprecia- 
tion, not  only  for  the  financial  assistance  rendered  but  more  es- 
pecially for  the  able  counsel  so  unstintedly  afforded. 

Acknowledgement  is  also  due  Mr.  V.  A.  Wallin  for  his  interest 
and  courtesy  in  making  possible  the  completion  of  the  experi- 
ments on  heavy  leathers. 

The  author  wishes  to  thank  sincerely,  Prof.  A.  H.  White  for 
his  constant  interest  and  hearty  co-operation  during  the  entire 
time  consumed  by  this  research. 

INTRODUCTION. 

The  use  of  hides  both  as  skins  and  leather  for  protection 
against  cold  and  rain,  for  weapons,  or  for  ornaments,  dates  back 
to  the  remotest  history  of  man. 

While  the  hides  were  tanned  in  the  earlier  times  with  the  hair 
on,  methods  were  soon  found  to  remove  it  and  thus  improve  the 
product.  The  first  substance  used  was  probably  wood  ashes  and 
this  continued  as  the  standard  for  some  time.  After  tanneries 
were  established,  for  up  to  this  time  the  tanning  was  done  only 
on  a  small  scale,  new  substances  were  sought  for,  and  lime,  one 
of  the  oldest  depilatory  agents,  was  used.  The  method  followed 
was  to  slack  the  lime  in  pits  and  soak  the  hides  in  a  saturated 
solution  of  calcium  hydroxide.  This  method  although  slightly 
modified  has  remained  practically  the  same  for  centuries. 

The  tanning  process  was  and  is  in  general  the  following: 

i.  Hides  are  soaked  to  remove  blood  and  dirt  and  to  bring 
them  back  as  nearly  as  possible  to  their  original  condition. 


4  A   STUDY   OF   TH£   CHANGES   IN    SKINS 

2.  They  are  placed  in  pits  containing  milk  of  lime,  bacteria 
being  always  present  and  sulphides  being  frequently  added,  for 
from  3  to  1 8  days  until  the  hair  "slips"  easily,  that  is,  can  be  easily 
removed. 

3.  They  are  then  bated  to  remove  lime  and  bring  the  skin  into 
the  desired  physical  condition.     The  bate  may  be  either  acid  or 
bacterial. 

4.  The  next  step  is  the  pickling  process  in  which  the  skins  are 
treated  usually  with  salt  and  sulphuric  acid. 

5.  Then   follows   the  tanning  process  proper,   which   may  be 
either  a  mineral  or  a  vegetable  tannage. 

6.  The  last  step  is  a  finishing  process. 

The  entire  tanning  process  has  thus  far  been  outlined  to  show 
the  dependence  of  the  finished  product  upon  the  correct  perform- 
ance of  each  succeeding  step  of  the  process.  It  is  only  through 
tests  on  the  finished  leather  that  the  effect  of  any  alteration  in 
any  step  of  the  process  can  be  detected. 

The  liming  process  is  the  one  studied  in  greatest  detail  in  this 
paper  but  any  changes  due  to  this  operation  can  be  detected  only 
in  the  finished  product.  Moreover,  the  method  of  soaking  must, 
because  of  its  influence,  also  be  specified.  The  object  of  soaking 
hides  is  to  cause  them  to  resume  as  nearly  as  possible  their  orig- 
inal clean  and  pliable  condition.  This  part  of  the  process  while 
not  so  important  when  green  hides  are  used  becomes  a  matter  of 
great  importance  when  dried  hides  are  to  be  investigated.  The 
length  of  soaking,  number  of  changes  of  water  and  the  acids  or 
alkalies  which  may  have  been  added,  all  have  an  effect  on  the  final 
product.  Should  the  hides  be  soaked  too  long  or  should  the  water 
not  be  renewed  frequently  enough,  bacteria  multiply  and  a  part 
or,  in  extreme  cases,  all  of  the  hide  may  be  lost.  On  the  other 
hand  acids  and  alkalies  cause  swelling  of  the  hide  and  if  too  much 
of  either  be  added  the  hide  will  be  "plumped"  too  much.1  This, 
while  not  fatal  to  a  good  final  product,  has  its  disadvantages  and 
as  a  rule  causes  trouble. 

The  object  of  liming  is  not  alone  the  removal  of  the  hair  but 
also  the  loosening  of  the  fiber  bundles.  More  surface  is  thus  ex- 
posed and  hence  the  tanning  agents  are  taken  up  more  readily. 
1  Jettmar  Handbuch,  p.  56. 


A   STUDY   OF   THE)    CHANGES   IN    SKINS  5 

In  the  vegetable  tannage  this  makes  a  heavier  leather.  In  the 
mineral  tannage  the  loosening  of  the  fiber  bundles  makes  a  more 
pliable  leather.2  The  latter  object  is  of  great  importance  in  the 
chrome  tannage  which  is  the  method  most  used  in  manufacturing 
light  or  upper  leathers.  The  hides  after  soaking  are  placed  in 
pits  in  which  an  excess  of  calcium  hydroxide  is  always  present 
and  to  which  some  sodium  or  arsenic  sulphide  may  or  may  not 
have  been  added.  The  hides  are  "hauled,"  that  is,  taken  out  and 
the  lime  "bettered"  once  a  day  until  the  hair  "slips"  easily.  It 
requires  much  practice  and  experience  before  one  is  able  to  tell 
exactly  whether  a  hide  is  done  or  not,  and  the  method  is  not  only 
unsatisfactory  but  also  very  unscientific,  for  the  personal  equa- 
tion of  the  operator  plays  too  important  a  part.  The  hides  are 
then  soaked  in  warm  water,  paddled  and  beamed.  In  the  latter 
process  the  skin  is  placed  over  a  piece  of  wood  semi-circular  in 
cross  section  and  the  hair  is  removed  with  a  blunt  knife.  The 
long  hairs  comes  off  very  easily  but  the  fine  or  "ground"  hair  and 
the  pigment,  especially  in  the  case  of  black  skins,  cause  some 
trouble.  Part  of  the  intercellular  substance,  corium,  "scud"  or 
"gneiss"  and  some  lime  soaps3  are  also  removed  in  this  treatment 

The  next  operation,  "bating,"  has  as  its  main  object  complete 
removal  of  the  lime  remaining  from  the  previous  treatment.  The 
loosening  of  the  fiber  bundles,  however,  is  also  materially  aided 
by  bating  and  this,  as  before  mentioned,  is,  in  the  case  of  light 
leather,  of  greatest  importance.  The  bates  most  commonly  used 
owe  their  activity  to  bacteria  and  are  frequently  more  or  less  un- 
satisfactory and  harmful  to  the  skins.  Bates  of  known  bacterial 
cultures  are  used  somewhat  and  give  good  results,  but  the  most 
common  ones  consist  of  organic  acids  such  as  butyric,  lactic,  etc. 

The  skins  are  then  pickled.  The  pickling  consists  usually  of  a 
treatment  with  sulphuric  acid  and  salt.  One  object  is  to  partially 
reduce  the  excessive  swelling  caused  by  the  bate.  Another, 
without  doubt,  is  to  furnish  some  free  sulphuric  acid  which  is 
considered  necessary  in  the  subsequent  chrome  bath.  This  sul- 
phuric acid  is  probably  absorbed  by  the  skin  and  thus  carried 
over  to  the  tan  bath.  This  finishes  the  treatment  received  by  the 

2  Gerber,  No.  938,  p.  253;  Procter's  Principles  of  Leather  Manufactur- 
ing, p.  126. 

3  Procter's  Principles  of  Leather  Manufacture,  p.  136. 


6  A   STUDY   OF   THE   CHANGES   IN    SKINS 

skins  in  the  "Beam  House,"  which  is  probably  the  most  im- 
portant division  of  the  tanning  process.  The  most  important  part 
of  the  beam  house  work  is  the  liming  process,  and  hence  this  was 
made  the  object  of  the  subsequent  investigations.  The  object  was 
to  gain  some  insight  if  possible,  into  this  apparently  simple  but 
actually  very  complicated  process  and  to  furnish  something  of 
practical  value  to  the  industry. 

It  seemed  obvious  that  some  accurate  way  of  controlling  the 
liming  and  of  judging  the  product  afterward  was  absolutely 
necessary  in  order  that  improvements  could  be  noted.  The  ordin- 
ary method  of  judging  the  product  by  the  "feel"  left  much  to  be 
desired  and  it  was  recognized  that  the  personal  equation  had  to 
be  eliminated  as  much  as  possible  if  anything  of  real  value  were 
to  result.  The  most  natural  idea  was  to  obtain  some  means  of 
following  the  action  of  the  lime  step  by  step.  This  could  not  be 
accomplished  with  the  naked  eye  and  hence  the  assistance  of  the 
microscope  was  necessary.  A  review  of  the  literature  at  hand 
showed  that  although  considerable  work  with  the  microscope  had 
been  done  the  results  were  not  very  satisfactory. 

STUDY  OF  MICROSCOPIC  CHANGES  IN  HIDES  DURING  THEIR 
CONVERSION  INTO  LEATHER. 

Some  of  the  earliest  work  on  the  cutting  of  sections  of  leather 
was  done  by  Kathreiner  in  1879.*  This  work  was  never  pub- 
lished and  on  inquiring  of  Prof.  Procter  it  was  found  that  al- 
though notes  had  been  preserved,  they  were  in  no  shape  to  allow 
of  their  being  published.  Thus  we  have  no  authentic  record  of 
his  work.  The  next  reference  found  was  to  some  work  by  Prof. 
Thomas  Palmer.5  He  applied  his  method  to  determine  the  pene- 
tration of  vegetable  tanning  agents.  The  sections  were  mostly 
cut  by  hand.  Some  sections  after  dehydration  in  alcohol  and 
clearing  in  clove  oil  were  infiltrated  with  "Strickers"  solution 
(gum  arabic  and  glycerine  3:1)  and  cut  with  a  microtome.  In 
some  cases  he  also  dehydrated  in  alcohol  two  or  three  hours, 
cleared  in  a  mixture  of  cedar  oil  and  benzol,  infiltrated  in  a  mix- 
ture one  part  50°  melting  point  and  two  parts  40°  melting  point 
paramne  until  transparent,  and  then  changed  to  a  bath  of  two 

4  Procter's  Leather  Industries  Laboratory  Book,  p.  424. 

5  Collegium,  1902,  p.  325. 


A   STUDY   OF   THE   CHANGES   IN    SKINS  7 

parts  50°  melting  point  and  one  part  40°  melting  point  paraffine 
for  three  or  four  hours.  The  mixture  of  cedar  oil  and  benzol 
was  in  the  ratio  of  three  to  five.  He  does  not  tell  of  any  changes 
noted  in  the  leather,  except  that  the  distance  to  which  the  tanning 
agent  had  penetrated  could  be  noted  by  differential  stains.  More- 
over he  does  not  give  the  thickness  of  the  sections  cut.  Procter, 
in  his  Leather  Industries  Laboratory  Book,  also  speaks  of  cut- 
ting sections  by  hand  and  of  cutting  sections  by  means  of  a  micro- 
tome, but  gives  no  specific  directions. 

M.  Henri  Boulanger  in  an  elaborate  monograph,  "Essais  du 
Cuir  dans  ses  Applications  industrielles.  Memoires  publics  par 
la  Societe  d'Encouragement  pour  1'industrie  national  1907,"  part 
of  which  is  published  as  "Etude  Micrograph ie  du  Cuir"  in  Bulle- 
tin de  la  Societe  d'Encouragement  in  1908,  gives  some  directions 
for  cutting  sections.  The  pieces  to  be  cut  are  placed  12  hours 
in  a  mixture  composed  of  distilled  water  5  grams,  pharmaceu- 
tical glycerine  5  grams,  acetone  90  grams.  They  are  then  dried 
and  imbedded  in  hard  paraffine  and  cut.  Another  method  given 
is  to  dehydrate  in  gradually  increasing  alcohol  until  absolute  is 
used,  to  place  in  xylol,  then  in  melted  paraffine  38°  to  40°.  After 
several  days  the  tissues  are  cooled,  dried  36  or  48  hours,  im- 
bedded in  hard  paraffine  and  cut.  Although  many  sections  were 
prepared  their  thickness  is  not  mentioned.  One  interesting  con- 
clusion of  the  author  is  that  the  elastic  fibers  are  well  preserved 
and  that  to  them  the  leather  owes  its  strength  and  pliability,  while 
the  connective  tissue  has  been  totally  changed.  This  is  a  remark- 
able conclusion  when  one  takes  into  consideration  that  less  than 
3  per  cent,  of  the  skin  is  elastic  tissue  and  more  than  95  per  cent, 
is  connective  tissue.6  Moreover  the  elastic  fibers  have  little  elas- 
ticity and  are  the  first  to  rupture  when  the  skin  is  stretched. 
Their  chief  function  appears  to  be  that  of  support.7 

Andreis,  in  an  article  on  "The  Process  of  Liming"8  speaks  of 
"taking  a  transverse  section  of  the  hide  and  noting  no  horizontal 
layers  or  channels."  He  does  not  give  any  methods  for  cutting 
the  sections  and  presumably  means  that  they  are  to  be  cut  by 
hand. 

6  Reimer,  Ding.  Poly,  fout..  No.  205,  p.  149  (1872). 

7  Hyde,  Diseases  of  the  Skin,  p.  22  (1909). 

8  JOURNAL,  Am.  Leather  Chem.  Assoc.,  Vol.  VII,  p.  609  (1912). 


8  A   STUDY   OF   THE   CHANGES   IN    SKINS 

As  none  of  the  references  quoted  gave  definite,  concise  and 
adequate  directions  for  preparing  sections,  experiments  were  re- 
sorted to,  in  order  to  find  a  way  to  prepare  good  sections  by  some 
simple  and  quick  method  Having  no  landmarks  to  guide  us, 
much  time  was  spent  in  going  astray.  At  this  time  certain  sec- 
tions of  rocks  were  being  made  by  grinding  and  this  method  ap- 
peared feasible  for  leather.  The  piece  of  leather  to  be  ground 
was  placed  in  Canada  balsam  in  a  tube  in  hot  water  and  suction 
applied.  After  two  to  four  hours  the  leather  seemed  impregnated 
with  balsam  and  was  removed,  mounted  on  a  piece  of  plate  glass 
I  inch  square  and  ground  with  a  carborundum  wheel  until  a 
flat  surface  was  obtained.  The  piece  was  then  turned  over  and 
mounted  and  the  grinding  continued,  until  the  section  was  fairly 
thin.  Then  a  finer  wheel  was  used,  until  the  section  became  very 
thin.  It  was  removed,  turned  over  and  mounted  on  a  glass  slide 
and  the  grinding  resumed,  until  the  section  was  as  thin  as  could 
be  obtained.  These  sections  showed  some  fiber  bundles  but  were 
unsatisfactory  in  three  ways.  The  process  was  too  slow,  the 
sections  too  thick,  and  a  complete  section  could  not  be  obtained  as 
some  parts  were  always  torn  away  in  grinding. 

METHODS  OF  IMBEDDING  AND  CUTTING  TISSUES. 
Leather  is  harder  and  tougher  than  ordinary  tissue.    It  is  dense 
and  requires  an  unusually  long  period  of  infiltration.     It  is  tough 
and  offers  great  resistance  to  the  knife  so  that  the  infiltration  must 
be  very  thorough  before  good  sections  can  be  obtained. 

Methods  of  cutting  sections  after  imbedding  in  paraffine  and 
celloidin  and  after  freezing  were  studied.  Various  modifications 
were  tried  and  those  giving  best  results  are  described  in  detail, 
although  they  are  merely  modifications  of  methods  used  in 
pathology. 

The  method  of  imbedding  in  paraffine  involves  the  following 
steps. 

i — 95  per  cent,  alcohol  24  hours,  change  after  12  hours. 

2 — Absolute  alcohol  24  hours,  change  after  12  hours. 

3— Xylol,  i  hour. 

4 — Xylol,  2  hours. 

5— Paraffine  42°  melted  in  an  oven  from  12  to  24  hours  depending 

on  size  of  piece  used. 
6 — Paraffine  52°  from  24  to  48  hours  depending  on  size  of  the  piece. 


A  STUDY  OF  THE;  CHANGES  IN  SKINS  9 

The  piece  is  then  taken  from  the  molten  paraffine  and  imbedded 
according  to  the  following  procedure.  A  small  dish  is  greased 
with  tincture  of  green  soap  or  glycerine  and  placed  in  cold  water. 
Clean  52°  paraffine  is  melted  with  a  free  flame  and  the  molten 
paraffine  is  allowed  to  drop  into  the  dish  until  it  has  attained  a 
depth  greater  than  the  thickness  of  the  piece  to  be  imbedded.  As 
soon  as  a  film  of  hardened  paraffine  has  formed  on  the  bottom  the 
tissue  is  removed  from  its  previous  bath  and  placed  face  down  in 
the  dish.  The  surface  of  the  melted  paraffine  is  now  cooled  by 
blowing  on  it,  and  as  soon  as  a  fairly  thick  film  has  formed  the 
whole  dish  is  plunged  into  ice  water. 

In  spite  of  all  precautions  taken  this  method  was  not  satisfac- 
tory. All  attempts  to  cut  sections  of  a  satisfactory  thickness  were 
unsuccessful  as  the  tissue  was  either  pulled  away  from  the  im- 
bedding material  or  was  torn  by  the  knife.  In  fact,  no  com- 
plete thin  section  could  be  obtained  by  this  method.  Other 
methods  based  on  paraffine  infiltration  using  acetone,  clove  oil,  oil 
of  bergamot  and  aniline  were  tried  and  the  results  were  unsatis- 
factory. Even  infiltration  with  paraffine  in  solution,  that  is,  in 
benzol  or  xylol,  gave  poor  results.  This  seems  to  show  that 
ordinary  methods  cannot  be  used  and  that  methods  like  the  one 
used  by  Boulanger0  "infiltrating  in  melted  paraffine  15  minutes 
and  then  blocking  in  hard  paraffine"  cannot  give  good  results. 

The  next  method  tried  was  the  celloidin  method.  In  this  the 
dehydration  was  carried  over  a  longer  period  so  that  the  presence 
of  any  moisture  was  precluded.  The  procedure  was  as  follows : 

i — 80  per  cent,  alcohol  12  hours. 

2 — 95  per  cent,  alcohol  48  hours,  changed  every  24  hours. 
3 — Absolute  alcohol  48  hours,  changed  every  24  hours. 
4 — Absolute  alcohol  and  ether  (equal  parts)  24  hours. 
5 — i  per  cent,  celloidin  96  hours. 
6 — 2  per  cent,  celloidin  120  hours. 
7 — 5  per  cent,  celloidin  168  hours. 

8 — 10  per  cent,  celloidin  6  days  to  2  weeks  depending  on  the  size  of 
sample  used. 

In  order  that  a  number  of  pieces  might  be  imbedded  simultan- 
eously they  were  held  in  clips  tied  to  strings,  which  led  through 
holes,  in  the  wooden  cover  of  a  shallow  dish.     This  dish  was  filled 
9  Bulletin  de  la  Societe  d' encouragement,  p.  250  (1907). 


IO  A   STUDY   OF   THE:   CHANGES   IN    SKINS 

with  a  10  per  cent,  solution  of  celloidin,  the  cover  put  on  and  the 
ether  and  alcohol  allowed  to  evaporate.  The  tissues  were  then 
cut  out,  trimmed  and  mounted  on  wooden  blocks.  They  were 
cut  in  a  microtome  under  a  constant  flow  of  80  per  cent,  alcohol. 
The  sections  obtained  by  this  method,  after  long  practice,  were  as 
thin  as  5  or  7  microns  and  averaged  about  10  to  18  microns. 
These  could  be  examined  even  with  an  oil  immersion  lens.  This 
method  while  giving  excellent  results  had  as  a  very  serious  dis- 
advantage the  long  time  necessary  for  good  results.  Many  at- 
tempts were  made  to  shorten  this  method  but  none  gave  good 
results.  A  very  long  time  is  absolutely  necessary  for  perfect 
infiltration. 

Believing  that  the  added  knowledge  gained  by  experience  might 
after  all,  enable  us  to  use  the  paraffine  methods,  these  were  again 
tried.  The  results  while  better  than  those  first  obtained,  still  left 
much  to  be  desired.  The  leather  tore  away  from  the  paraffine 
very  easily  and  it  was  impossible  to  cut  good  sections.  The 
paraffine  methods  had  so  many  advantages  both  as  to  quickness 
and  simplicity,  that  many  modifications  of  the  method  previously 
given,  were  repeatedly  tried.  The  conclusion  finally  reached 
was,  that  none  of  the  paraffine  methods  would  give  good  results. 
Methods  using  beeswax,  gum  arabic,  etc.,  were  tried  and  also 
failed  to  give  good  results. 

The  only  short  method  which  appeared  promising  was  the 
freezing  method  and  this  was  then  tried.  This  method  had  the 
obvious  advantage  of  great  saving  in  the  time  required  to 
obtain  complete  sections.  The  method  was  very  simple  and, 
although  much  practice  and  experience  were  necessary  before 
good  sections  were  obtained,  the  results  justified  the  time  spent 
in  acquiring  the  technique.  The  sample  to  be  sectioned  was  cut 
from  calfskins,  i  by  2  centimeters  and  if  wet,  mounted  directly. 
If  dry,  it  was  first  soaked  in  water  until  thoroughly  moistened 
and  then  mounted  upon  the  base  plate  of  a  Bardeen  microtome 
and  covered  with  a  thick  solution  of  gum  arabic.  The  liquid 
carbon  dioxide  was  then  turned  on  and  the  pieces  were  frozen 
very  gradually.  When  the  right  degree  of  hardness  has  once  been 
obtained  the  piece  should  never  be  allowed  to  warm  up  and  should 
never  be  frozen  again.  This  is  of  great  importance  as  several 


A   STUDY   OF   THU   CHANGES   IN    SKINS  II 

freezings  will  cause  important  changes  in  the  structure.10  The 
greatest  changes  are  caused  by  over  freezing  and  if  this  is  done 
excessively,  the  piece  used  may  crumble  and  become  worthless. 
A  slight  fixation  of  the  tissue  in  10  per  cent,  formol11  prevents 
most  of  the  changes  due  to  freezing.  The  sections  when  cut 
are  placed  in  a  dish  filled  with  water.  They  are  then  transferred 
by  means  of  a  brush  or  section  lifter  to  a  10  per  cent,  dextrin 
solution  which  is  kept  warm,  and  floated  onto  a  glass  plate,  dried 
a  few  minutes,  soaked  in  absolute  alcohol  until  clear  and  coated 
by  pouring  over  them  a  I  or  2  per  cent,  solution  of  celloidin. 
The  plates  are  placed  in  warm  water  and  left  until  the  thin 
celloidin  sheet  floats  off.  They  can  now  be  handled  easily  and 
quite  roughly  without  any  danger  of  damage.  They  can  be 
stained  with  alcoholic  or  aqueous  solutions  of  various  dyes.  A 
water  solution  of  eosin  and  also  a  double  stain,  first  in  Weigert's 
haematoxylin  and  then  in  Van  Giesens12  mixture  were  used.  The 
latter  gave  excellent  results  and  enabled  one  to  distinguish  the 
various  kinds  of  fibers  present,  with  great  certainty. 

The  sections  were  not  so  thin  as  those  obtained  by  the  celloidin 
method,  averaging  only  35  to  40  microns,  but  this  was  thin  enough 
to  allow  the  use  of  any  high  power  objectives  except  the  oil 
immersion.  The  sections  were  very  delicate  and  required  great 
care  in  the  preliminary  handling.  The  method  requires  little 
time.  A  skilled  operator  can  fix,  freeze,  stain  and  mount  a  com- 
plete section  in  30  or  40  minutes.  In  some  cases  the  time  required 
is  greater  depending  on  the  ease  with  which  the  piece  in  question 
can  be  cut.  Sections  from  heavy  hides  during  the  liming  require 
much  longer,  as  the  tissue  is  very  delicate  and  flabby  and  tears 
very  easily.  After  the  hide  has  been  in  a  tan  liquor  it  can  be 
cut  very  rapidly.  This  method  has  not  only  the  advantage  of 
speed  but  also  is  better  in  that  the  tissue  is  practically  the  same 
as  it  was  before  cutting.  The  method  does  not  subject  the  tissue 
to  such  severe  treatment  as  for  instance  the  dehydration  with 
absolute  alcohol,  which  is  necessary  in  the  case  of  the  celloidin 
and  paraffine  methods.  It  is  true  that  freezing  may  dehydrate 
in  a  certain  sense,  but  the  following  immersion  in  water  probably 

10  Warlhin  Practical  Pathology,  p.  215. 

11  Warthin  Practical  Pathology,  p.  216. 

12  Warthin  Practical  Pathology,  p.  260. 


12  A   STUDY   OF   THE;   CHANGES   IN    SKINS 

allows  the  tissue  to  resume  its  previous  condition.  This  seems 
logical,  since  the  freezing  lasts  a  very  short  time,  from  5  to  10 
minutes  at  the  most. 

STUDY  OF  CHANGES  IN  STRUCTURE  DURING  TANNING. 

Before  proceeding  to  the  experimental  study  of  tissues  prepared 
in  the  laboratory  a  considerable  number  of  commercial  products 
were  examined.  Sections  were  made  of  various  commercial 
leathers  such  as  dongola,  waterproof,  wax  upper,  plow  grain, 
flesh  splits,  badger  sides,  oil  grain,  reliance  calf,  dull  romar 
sides,  kangaroo  calf  and  others.  These  gave  some  idea  of  how 
a  finished  leather  looked.  Through  the  courtesy  of  Mr.  Carl  E. 
Schmidt  of  Detroit,  pieces  were  cut  daily  from  a  particular 
calfskin  as  it  went  through  his  tanning  process  and  sent  for 
examination.  As  soon  as  these  samples  were  received  a  section 
was  made  by  the  freezing  method  and  a  piece  started  by  the  slow 
celloidin  method.  This  set  was  kept  as  a  standard  of  a  good 
product  and  will  be  referred  to  as  S-22.  This  set  did  not,  however, 
entirely  fulfill  its  purpose,  because  the  necessity  of  knowing  the 
exact  location  and  orientation  of  the  pieces  cut  from  the  hide 
was  not  discovered  until  later.  This  was  shown  by  an  examination 
of  pieces  cut  in  a  systematic  manner  from  a  finished  calfskin 
(Experiment  S-i8).  Samples  were  taken  from  this  leather  at 
the  butt,  right  and  left  flank,  and  neck  and  carefully  infiltrated 
with  celloidin.  Sections  were  cut  both  parallel  and  at  right 
angles  to  the  grain.  The  sections  showed  a  great  difference  in 
structure  between  pieces  cut  from  the  flank  and  from  the  butt. 
These  show  the  flank  to  have  a  much  smaller  amount  of  connective 
fibers  than  the  butt  and  neck.  Moreover,  the  fiber  bundles  of  the 
flank  are  further  apart  and  in  general  form  a  looser  network. 
The  connective  tissue  is  more  wrinkled  that  is,  the  folds  in  the 
individual  fiber  bundles  are  more  numerous.  This  apparently 
accounts,  at  least  partially,  for  the  looseness  of  the  flank  after 
tanning. 

This  difference  between  various  portions  of  the  same  skin  was 
further  studied  in  series  S-26,  by  tanning  two  pieces  of  calfskin 
cut  so  that  one  piece  was  almost  entirely  flank  while  the  other 
was  along  the  backbone.  Small  pieces  were  cut  daily  from  adja- 
cent portions  of  each  skin,  one  from  the  backbone  and  the  other 


A    STUDY   OF   THE   CHANGES   IN    SKINS  13 

from  the  edge  of  the  flank,  and  sections  were  prepared  by  the 
freezing  method  using  the  Van  Giesen  stain.  Sections  were  cut 
both  parallel  and  at  right  angles  to  the  backbone  in  each  instance. 
These  showed  the  same  looseness  in  structure  in  the  fresh  flank 
as  was  evident  in  the  finished  leather. 

This  subject  was  pursued  still  more  systematically  in  Series 
8-36  where  a  whole  calfskin  was  trimmed  to  an  approximate 
rectangle  and  divided  into  six  pieces.  This  work  is  referred  to 
again  in  the  discussion  of  volume  changes  where  the  details  are 
given. 

Through  the  courtesy  of  V.  A.  Wallin  of  Grand  Rapids,  samples 
of  a  certain  cow  hide  were  sent  throughout  the  tanning  process. 
The  pieces  were  taken  so  that  the  sections  made  therefrom  could 
be  cut  parallel  and  at  right  angles  to  the  backbone.  Samples 
were  received  during  the  following  stages  of  the  tanning  process. 
All  sections  were  cut  by  the  freezing  method. 

No.     i. — Washed  hide — originally  a  green  salted  one. 

No.    2. — After  24  hours  in  lime. 

No.    3. — After  72  hours  in  lime. 

No.    4. — After  96  hours  in  lime. 

No.    5. — Out  of  hot  water. 

No.    6. — Into  cold  water. 

No.    7. — Out  of  cold  water. 

No.    8. — Out  of  rockers — in  8  days. 

No.    9. — Out  of  hang  yard — in  4  days. 

No.  10. — Out  of  first  layer — in  5  days. 

No.  ii. — Out  of  second  layer — in  9  days. 

No.  12. — Out  of  third  layer — in  15  days. 

No.  13. — Out  of  fourth  layer — in  22  days. 

No.  14. — Out  of  fifth  layer — in  28  days. 

No.  15. — Out  of  wet  dip — in  15  days. 

No.  16. — Out  of  tempering  vats — in  2  days. 

No.  17.— Out  of  bleach. 

No.  18.— Out  of  oil  wheel. 

No.  19. — Finished  leather. 

In  these  various  experiments  about  125  different  blocks  were 
prepared,  from  which  600  specimens  were  cut,  stained  and 
mounted.  A  careful  examination  of  all  these  sections  gave,  how- 
ever, rather  meager  results.  The  changes  from  day  to  day  are 
so  gradual  and  the  differences  in  structure  of  different  portions 
of  the  same  hide  are  so  pronounced  that  it  is  extremely  difficult 


14  A   STUDY   OF   THE   CHANGES.  IN    SKINS 

to  state  the  cause  for  any  differences  observed.  The  fiber  bundles 
become  partially  separated  into  fibrils  in  the  liming  process,  but 
it  could  not  be  determined  whether  these  fibrils  are  hollow  or 
solid.  In  the  bark-tanned  process  the  interstices  become  filled 
with  solid  material  so  that  the  leather  becomes  firm  and  of  more 
uniform  structure.  In  chrome-tanned  leather,  the  interstitial 
spaces  are  even  greater  than  in  the  soaked  hide  and  the  fiber 
bundles  and  fibrils  are  sharply  defined.  The  flank  is  undoubtedly 
composed  of  larger  fiber  bundles  than  the  butt  or  shoulder  and 
in  the  former  there  are  larger  spaces  between  these  bundles  than 
in  the  latter. 

The  idea  first  held  that  the  microscopic  method  could  be  used 
in  the  tannery,  as  an  accurate  check  on  the  process,  had  to  be 
abandoned.  The  great  difficulty  was  that  in  a  given  skin,  pieces 
from  different  parts  showed  such  differences  in  structure  that 
even  after  long  experience  one  could  not  tell  whether  the  differ- 
ences shown  were  inherent  in  the  skin  or  due  to  the  influence  of 
the  treatment. 

CHANGES  IN  VOLUME  OF  HIDES  DURING  LIMING  PROCESS. 

Changes  in  the  volume  of  hides  in  the  limes  are  so  great  as  to- 
be  readily  noticed.  There  have,  however,  been  no  quantitative 
data  published  on  this  point.  The  apparatus  used  for  these 
measurements  is  shown  in  Fig.  I. 

It  consists  of  a  brass  cylinder  A,  2.5  inches  in  diameter  and 

15  inches  high.    At  the  bottom  a  small  brass  tube  B,  0.25  inch  in 
diameter  leads  to  an  upright  100  cc.  glass  stoppered  burette,  C. 
The  cover  D  screws  on  to  the  cylinder  by  means  of  a  very  fine 
thread,  which  insures  a  water-tight  joint.     The  cover  is  divided 
into  30  equal  divisions  on  the  edge  K  and  a  vertical  mark  is  made 
on  the  cylinder,  permitting  the  cover  to  be  screwed  down  to  a 
definite  point  or  reading.     In  the  center  of  the  cover  a  hole  is. 
bored   into  which   a  pipe  with   outside  threads   H   is   soldered. 
Another  pipe  with  inside  threads  F  fits  over  B.    A  glass  tube  G 
with  a  fine  string  around  it  is  inserted  into  H  through  F  and 
screws  tight  by  means  of  F.    This  joint  is  also  water  tight,  if  the 
thread  has  been  previously  greased.     The  threads  of  cover  D 
are  also  greased,  anhydrous  lanoline  proving  a  good  material  for 
this  purpose.    The  glass  tube  G  has  a  mark,  to  which  the  liquid: 


A   STUDY   OF   THE   CHANGES   IN    SKINS  1 5 

used  is  allowed  to  ascend  before  a  reading  is  taken.  This  is  done 
by  keeping  burette  C  filled  to  a  mark,  higher  than  the  top  of  the 
cylinder.  The  cylinder  is  lacquered  on  the  inside  and  can  be  used 
for  lime. 


FIG.  1. 


To  obtain  some  idea  of  the  accuracy  of  the  measurements  made, 
the  following  experiments  on  the  volume  of  a  glass  stopper  are 
given  : 

Number  of  test I  II 

Zero  reading  in  cc 25.45  5&9 

Taken  out  in  cc 50.00  o.o 

Total  cc 75.45  58.9 

Final  reading  34-5O  17.9 

Volume  in  cc 40.95  41.00 

The  average  volume  was  40.93  cc.  and  the  maximum  error  was 
o.i 8  cc.  in  40.93  cc.  equaled  0.44  per  cent.  This  error,  however, 
was  relatively  small  because  the  stopper  could  be  dried  and 


in       rv        v 

20.70  59.85  57.65 

50.0  o.o       o.o 

70.70  59.85  57.65 

29.95  18.90  16.65 

40.75  40.95  41.00 


l6  A   STUDY   OF   TH£   CHANGES   IN    SKINS 

always  brought  to  a  certain  condition  of  surface  moisture,  not  a 
varying  one,  as  was  the  case  with  skins.  The  removal  of  liquid 
which  was  made  necessary  whenever  the  volume  exceeded  about 
50  cc.  was  best  accomplished  by  means  of  a  pipette.  The  liquid 
was  drawn  up  into  the  burette  after  a  measurement  had  been 
taken,  by  means  of  a  rubber  tube  attached  to  the  burette  and  to 
a  suction  pump.  The  procedure  was  as  follows:  Some  of  the 
liquid  to  be  used  was  put  into  the  cylinder  A  and  the  burette  filled 
by  applying  suction.  The  stop  cock  was  closed,  the  cylinder  filled 
and  the  cover  screwed  down  to  a  certain  mark.  The  stop  cock 
was  then  opened  and  the  liquid  allowed  to  run  into  the  cylinder 
until  the  meniscus  in  the  glass  tube  G  was  even  with  the  mark. 
A  reading  of  the  burette  gave  the  zero  reading.  The  liquid  was 
sucked  back  into  the  burette,  the  cover  taken  off,  the  sample 
placed  in  the  cylinder  and,  if  the  volume  was  large,  some  of  the 
liquid  was  pipetted  off.  The  cylinder  was  then  closed  and  a  read- 
ing taken  as  before.  This  gave  a  final  reading  and  from  it  and 
the  zero  reading  the  volume  was  easily  calculated.  The  skin  to 
be  measured  was  always  dried  with  a  moist  cotton  cloth  which 
was  wrung  as  dry  as  possible.  The  skin  was  always  measured 
in  the  same  liquid  in  which  it  was  at  that  stage  of  the  experiment, 
that  is,  when  in  the  limes,  in  lime  water ;  when  in  pickle,  in  pickle 
solution,  etc.  Duplicate  determinations  on  pieces  of  skin  whose 
volume  was  from  200  to  400  cc.  agreed  within  about  I  cc.  When 
dry  skins  were  to  be  measured  the  cylinder  was  filled  with  water. 
The  skin  naturally  absorbed  some  water,  but  if  the  experiment 
was  performed  rapidly,  the  error  was  not  large,  as  was  shown  by 
the  following  experiment : 

Zero  reading 56.75 

Final  reading  14.25 


Volume 42.50  after  I  minute 

42.65  after  2  minutes 

42.85  after  3  minutes 

42.70  after  4  minutes 

42.95  after  5  minutes 

43.00  after  10  minutes 

43.1  after  15  minutes 
43.3    after  20  minutes 

The  change  in  volume  due  to  water  absorption  is  very  small. 


A   STUDY   OF   THE   CHANGES    IN    SKINS  \J 

To  test  the  absolute  accuracy  of  the  method  this  same  piece  of 
skin  was  dried  and  its  volume  remeasured.  The  agreement  was 
within  0.5  cc.  One  difficulty  to  be  guarded  against  in  measuring 
dry  skins  is  the  tendency  of  air  bubbles  to  adhere  to  the  hairs. 
This  can  be  avoided  by  shaking  the  whole  apparatus  just  prior 
to  taking  measurements. 

Ex  PERI  MENTAL,  WORK  ON  VOLUME  CHANGES  OF  CALFSKINS. 

Nine  sets  of  tests  involving  measurements  of  volume  changes 
on  twenty-one  different  pieces  of  skin  are  reported  here.  Micro- 
scopic sections  from  some  of  these  sets  have  been  referred  to 
previously.  The  full  data  are  given  under  the  separate  headings, 
but  the  sets  may  be  outlined  as  follows : 

8-25 — A  half-calfskin  split  along  the  backbone  and  trimmed, 
cut  into  three  pieces  of  about  equal  size  at  right  angles  to  the 
backbone.  Carried  through  the  tanning  process.  Changes  in 
weight  of  the  pieces  were  also  noted  and  the  density  at  each  stage 
computed. 

8-26 — A  half  calfskin  as  above  was  carried  through  the  whole 
process  as  one  unit.  Measurements  of  surface  area  and  weight 
were  included. 

8-27 — A  piece  of  calfskin  carried  through  the  limes  only. 

8-28 — Duplicate  of  26. 

8-29 — A  half  calfskin  was  cut  parallel  to  the  backbone  to 
make  one  piece  back  and  the  other  flank.  Carried  through  the 
limes. 

8-31 — Duplicate  of  29,  but  carried  only  through  soaking 
process. 

8-36 — A  whole  calfskin  trimmed  and  cut  into  six  pieces.  Pro- 
tective action  of  lime  soap  tasted. 

8-39 — Duplicate  of  25. 

8-396 — Duplicate  of  29. 

EXPERIMENT  8-25. 

A  dry  salted  calfskin  was  split  along  the  backbone  and  one  half 
was  trimmed  and  cut  into  three  pieces  of  about  equal  size  at  right 
angles  to  the  backbone.  The  piece  nearest  the  head  was  marked 
I,  the  middle  piece  II,  and  that  nearest  the  tail  III.  These  pieces 
were  soaked  in  water  three  days,  the  water  being  changed  every 
12  hours.  They  were  then  placed  in  limes,  made  by  using  5, 


iS 


A    STUDY   OF   THE   CHANGES   IN    SKINS 


grams  of  slaked  lime  to  400  cc.  of  water,  a  portion  of  old  lime 
being  added  to  inoculate  the  new  lot.  It  was  bated  in  a  bran 
drench  and  pickled  in  salt  and  sulphuric  acid  solution  made  by 
taking  3  grams  of  concentrated  sulphuric  acid  and  36  grams  of 
salt  in  850  cc.  of  water.  The  tannage  was  by  Dennis's  one-bath 
chrome  method.  In  the  following  tables  and  curves  the  changes 
in  volume  and  weight  are  calculated  on  the  volume  and  weight  of 
the  skin  after  72  hours  soaking  in  water  instead  of  on  the  dry 
skin.  This  follows  the  usual  custom  of  basing  all  computations 
on  the  wet  hide  and  allows  comparison  to  be  made  with  green 
hides. 


EXPERIMENT  8-25.— CHANGES  IN  DENSITY. 


Condition  of  skin.             Nu 
In  water  72  hours  

mber  I 
.08 
.09 
.08 
.08 

•05 
.06 
.07 
.07 
.07 
.07 
.04 
.06 
.06 

Number  II 
1.  10 

1.  10 

1.  06 
1.09 
1.05 
1.07 
1.  08 
1.  08 
1.07 
1.05 

1.  06 
I.O7 

In  lime  24  hours  

In  lime  48  hours  

In  lime  72  hours  

In  lime  96  hours  

In  lime  120  hours  

In  lime  144  hours  

In  lime  168  hours   
In  lime  192  hours  

Unhaired  and  fleshed  •  •  • 

p.  ,  ,    , 

Tanned  . 

Number  III 
.12 


•05 
•03 
.04 
.10 
.09 
.08 


EXPERIMENT  8-26. 

A  dry  salted  calfskin  was  trimmed  and  split  along  the  back- 
bone. It  was  intended  to  carry  a  half -skin  through  the  experi- 
ment as  one  piece  but  the  apparatus  for  volume  measurements 
was  found  to  be  too  small  so  it  was  split  into  two  pieces.  The 
figures  for  the  two  pieces  have  been  added  together  so  that  the 
result  is  reported  as  if  it  had  been  kept  as  one  piece.  Measure- 
ments are  reported  on  volume,  weight,  area  and  density  through- 
out the  tanning  process.  These  pieces  were  soaked  for  24  hours 
in  water,  the  latter  being  changed  after  12  hours.  The  lime  used 
was  made  by  dissolving  5  grams  of  dry  hydrated  lime  in  400  cc. 
of  water.  The  pieces  were  placed  in  this  solution  for  ten  days. 
The  lime  was  changed  every  48  hours  and  a  new  lime  of  the 
same  concentration  was  prepared.  After  liming  until  the  hair 
slipped  easily,  the  skins  were  placed  in  warm  water  for  a  few 
minutes,  unhaired  and  fleshed. 


A   STUDY   OF   THE)    CHANGES   IN    SKINS 


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A    STUDY   OF   THE)   CHANGES   IN    SKINS 


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22 


A   STUDY   OF   THE   CHANGES   IN    SKINS 

EXPERIMENT  25.— DENSITY. 


EXPERIMENT  25.— WEIGHT. 
Per  cent,  increase  on  third  soaked  weight. 


A    STUDY   OF   TH£   CHANGES   IN    SKINS 


EXPERIMENT  25.— VOLUME. 
Per  cent,  increase  on  third  soaked  volume. 


i 


1 


7     3 


EXPERIMENT  26.— VOLUME. 
Per  cent,  increase  on  24-hour  soaked  volume. 


A   STUDY   OF   THE   CHANGES   IN    SKINS 

EXPERIMENT  26.— WEIGHT. 
Per  cent,  increase  on  24-hour  soaked  weight. 


EXPERIMENT  26.— DENSITY. 


A    STUDY   OF   THE:   CHANGES   IN    SKINS  25 

The  samples  were  bated  three  hours  in  an  N/io  solution  of 
lactic  acid,  in  a  drum.  They  were  pickled  about  five  hours  in 
an  N/5O  solution  of  salt  and  sulphuric  acid.  They  were  then 
placed  in  a  drum  with  a  normal  salt  solution  for  one  hour  and 
chrome-tanned  by  the  one-bath  process.  Sections  were  also  cut 
daily  during  this  series,  as  has  been  mentioned  in  the  discussion 
of  the  microscopic  study.  The  results  are  given  in  the  accom- 
panying table  and  curves. 

EXPERIMENT  8-27. 

In  this  test  a  piece  of  dry  salted  calfskin  was  used.  It  was 
soaked  in  water  24  hours.  The  water  was  changed  after  12  hours. 
A  lime  solution  containing  5  grams  of  slaked  lime  in  400  cc.  of 
water  was  used  to  unhair  the  skin.  The  hide  was  in  the  limes 
seven  days.  Sections  and  volume  measurements  were  made  daily 
and  the  results  tabulated. 

EXPERIMENT  8-27  CHANGES  IN  VOLUME,  WEIGHT  AND  DENSITY. 

Volume      Increase    Per  cent.  Weight  Increase  Per  cent. 
Condition  of  the  skin     in  cc.  in  cc.        increase     in  g.        in  g.        increase    Density 

Dry  salted 83.3  — 154.6  —65.0  92  — 169  — 64.7 

In  water  24  hours-  237.9  o.o  o.o  26 r  o.o  o.o 

In  lime  24  hours..  335.6  97.7  41.1  380  119  45.6 

In  liuie  48  hours..  356.2  118.2  49.8  374  113  43.3 

In  lime  72  hours..  354.1  116.2  48.9  365  104  39.9 

In  lime  144  hours-  342.4  104.5  44.0  360  99  37.9 

In  lime  168  hours-  343.6  105.7  44.5  357  96  36.8 

EXPERIMENT  S-28. 

In  this  experiment  a  piece  of  dry  salted  calfskin  was  used.  The 
piece  of  skin  was  soaked  in  water  24  hours,  the  latter  having 
been  changed  after  12  hours.  The  limes  used  were  of  the  same 
concentration  as  in  Experiment  26.  The  pieces  of  hide  were 
limed  6  days.  Volume,  weight  and  area  measurements  were 
made  daily.  The  skins  were  limed,  unhaired  and  fleshed,  bated 
in  an  N/io  solution  of  lactic  acid  and  followed  by  a  bran  in- 
fusion. They  were  pickled  in  an  N/5O  solution  of  sulphuric  acid 
and  salt  and  tanned  by  the  method  given  in  the  previous  experi- 
ment. The  product  was  fair.  Analysis  showed  5.6  per  cent,  ash 
while  a  standard  sample  had  5.0  per  cent.  ash.  The  measure- 
ments taken  are  in  the  following  table.  The  increase  and  per- 
centage increase  in  weight  and  volume  are  all  computed  on  the 
volume  and  weight  after  24  hours  soaking  in  water. 


.10 

.10 
.12 
•05 
•03 
•05 
.04 


26 


A   STUDY   OF   TH£   CHANGES   IN    SKINS 


&~ 


EXPERIMENT  27. 
Per  cent,  increase  on  24-hour  soaked  volume  and  weight. 


I* 

Sto 


so 


EXPERIMENT  27.— DENSITY. 


A   STUDY   OF   THE   CHANGES   IN    SKINS  27 

EXPERIMENT  8.28  CHANGES  IN  VOLUME,  WEIGHT,  AREA 
AND  DENSITY. 

Per  In-        Per 

Volume  Increase    cent.     Weight  crease    cent.       Area  in 


Condition  oi 
Dry  salted 

the  skin 

in  cc. 
122.6 

in  cc. 
—  181.7 

increase 
—59-7 

in  g. 
135 

in  g. 

increase 
—58.6 

sq.  in.    E 
135 

>ensi 
.10 

In  water  24  hours  . 

304.3 

0.0 

O.O 

326 

O.O 

o.o       161 

.07 

In  lime  24 

hours  •  • 

427.2 

122.9 

40.3 

474 

148 

45 

•4 

161 

.11 

In  lime  48 

hours  .  . 

453-2 

148.9 

48.8 

482 

•      156 

47 

-9 

165 

.06 

In  lime  72 

hours  -. 

454-2 

149.9 

49-3 

483 

157 

48 

.1 

163 

.06 

In  lime  96 

hours  •  • 

455-1 

150.8 

49-5 

484 

158 

48 

-5 

164 

.06 

In  lime  120 

hours  . 

476.0 

I7I.7 

56.5 

501 

175 

53 

-7 

164 

•05 

In  lime  144 

hours  . 

463.0 

158.7 

52.1 

497 

I7I 

52 

-5 

160 

-07 

Unhaired  and  fleshed  220.  2 

—  84.1 

-27.6 

231 

-  95 

—29 

.1 

178 

•05 

Bated    .... 

184.5 

—  II9.8 

—39-3 

192 

—T34 

—41 

.1 

1.04 

Pickled 

129.3 

—175-0 

CTP    c 

145 

-181 

—55 

-5 

166      i.  12 

o/o 

Chrome  tanned  

142.5 

—  161.8 

—53-1 

158 

—  168 

—5i 

5 

151       i.  ii 

EXPERIMENT  8-29. 

In  order  to  show  whether  the  flank  absorbs  more  water  than 
the  butt,  a  piece  of  each  kind  was  used  in  this  experiment.  Num- 
ber one  was  a  piece  of  calfskin  butt  and  number  two,  a  piece  of 
flank  from  the  same  skin.  These  pieces  were  always  treated  in 
the  same  manner,  in  the  same  solutions.  The  hides  were  soaked 
48  hours  in  water,  this  being  renewed  every  12  hours.  The  limes 
contained  5  grams  slaked  lime  per  400  cc.  of  water.  The  liming 
continued  for  4  days  and  during  this  time  volume  measurements 
were  made  daily.  The  results  follow : 

EXPERIMENT  8-29. — CHANGES  IN  VOLUME  OF  BUTT  AND  FLANK. 

Number  I,  butt  Number  II,  flank 


Volume  Per  cent.  Volume  Per  cent. 

Condition  of  the  skin  in  cc.  increase  in  cc.  increase 

In  water  48  hours 87.1  134-8 

In  lime  24  hours 126.2  44.8  208.4  54«7 

In  lime  72  hours 138.2  58.8  244.8  82.2 

In  lime  96  hours 141.7  62.7  258.4  92.0 

EXPERIMENT  8-33. 

The  following  experiment  was  made  with  pieces  of  dry  salted 
calfskin.  Two  pieces  were  taken;  number  one  being  from  the 
flank  and  number  two  from  the  butt.  The  hides  were  soaked 
24  hours  in  water,  this  being  changed  after  12  hours.  The 
volume  was  measured  before  and  after  soaking. 


28 


A   STUDY   OF   TH£   CHANGES   IN    SKINS 


EXPERIMENT  28.— VOLUME. 
Per  cent,  increase  on  24-hour  soaked  volume. 


EXPERIMENT  28.— DENSITY. 


A  STUDY  OF  THE;  CHANGES  IN  SKINS 


29 


EXPERIMENT  28.— WEIGHT. 
Per  cent,  increase  on  24-hour  soaked  weight. 


if 


a 


EXPERIMENT  29.— VOLUME. 
Per  cent,  increase  on  48-hour  soaked  volume. 


A   STUDY    OF   THE:   CHANGES    IN    SKINS 


EXPERIMENT  8-33.— CHANGES  IN  VOLUME  OF  FLANK  AND  BUTT 
DURING  SOAKING. 

Number  I,  butt  Number  II,  flank 


Volume  Percent. 
Condition  of  the  skin        in  cc.     increase 


Volume  Percent. 
Condition  of  the  skin        in  cc.    increase 


Dry  salted 60.4  Dry  salted 56.2 

After  24  hours  in  water  75.4         25          After  24  hours  in  water  81.2         45 

EXPERIMENT  8-396. 

This  experiment  was  made  to  confirm  the  results  of  Experi- 
ment 8-29.  Two  pieces  of  dry  salted  calfskin  were  soaked  for 
48  hours  in  water,  which  was  changed  every  12  hours.  The 
pieces  were  limed  in  a  solution  of  5  grams  of  lime  in  400  cc.  of 
water,  for  5  days.  They  were  unhaired  and  fleshed,  bated  with 
lactic  acid,  pickled  with  sulphuric  and  salt,  and  chrome  tanned 
in  the  same  manner  as  stated  in  Experiment  8-28.  One  piece  was 
from  the  butt,  No.  i,  the  other,  No.  2,  was  from  the  flank.  Vol- 
ume measurements  were  taken  daily  and  the  results  tabulated. 

EXPERIMENT  8-396  CHANGES  OF  VOLUME  OF  BUTT  AND  FLANK. 

Number  I,  butt  Number  II,  flank 


Volume 

Increase 

Per  cent. 

Volume 

Increase 

Per  cent. 

Condition  of  the  skin 

in  cc. 

in  cc. 

increase 

in  cc. 

in  cc. 

increase 

Dry  salted 

45-3 

—  31-! 

—40.7 

45-3 

-42-5 

-48.5 

In  water  24  hours  

72.8 

-3-6 

—  4-1 

84.4 

—  3-4 

—  3-9 

In  water  48  hours  

76.4 

o.o 

O.O 

87.8 

o.o 

o.o 

In  lime  24  hours  

103.8 

27.4 

35.8 

"7-5 

29.7 

33-8 

In  lime  48  hours  

II0.2 

33-8 

44.2 

125-9 

38.1 

43-4 

In  lime  96  hours  

II9.I 

42.7 

55-9 

143.2 

55-4 

63-1 

In  lime  120  hours  

122.5 

46.1 

60.3 

150.2 

62.4 

71.1 

Unhaired  and  fleshed 

61.3 

—I5-I 

-19.8 

81.3 

-  6.5 

-  7-4 

"Rflrpri 

51-8 

—  24.6 

—32.2 

68.8 

—  19.0 

—21.6 

Pickled  

42.0 

—34-4 

—  45-° 

52.5 

-35-3 

—  40.2 

Chrome  tanned  .  . 

«..« 

2A.Q 

—  12.6 

62.7 

—  2t;.T 

—28.6 

EXPERIMENT  8-39. 

This  is  in  general  a  duplicate  of  Experiment  8-25.  Three 
pieces  of  dry  salted  calfskin  were  limed  in  a  solution  of  5  grams 
of  slaked  lime  in  400  cc.  as  in  previous  experiments,  and  volume 
and  weight  measurements  made  daily.  The  results  follow  in 
table,  Experiment  8-39.  The  increase  and  percentage  increase 
in  weight  and  volume  are  computed  on  the  weight  and  volume 
of  the  skin  after  48  hours  soaking  in  water,  respectively. 


A   STUDY   OF   THE)   CHANGES   IN    SKINS  3! 

/ 

EXPERIMENT  8-39.— CHANGES  IN  VOLUME,  WEIGHT  AND  DENSITY 

OF  SHOULDER. 
Number  I. 


Volume 

Increase 

Per  cent. 

Weight 

Increase 

Per  cent. 

Condition  of  the  skin 

in  cc. 

in  cc. 

increase 

ing. 

ing. 

increase 

Density 

Dry  salted 

150.6 

—  107.7 

—41.7 

— 

— 

— 

In  water  24  hours. 

253-0 

-5.3 

—  2.1 

— 

— 

— 

In  water  48  hours. 

258.3 

o.o 

O.O 

287 

O.O 

O.O 

I 

.11 

In  lime  24  hours.. 

346.0 

87.7 

34-o 

384 

97.0 

33.8 

I 

.11 

In  lime  48  hours.  . 

380.5 

122.2 

47-3 

418 

131 

45-6 

I 

.10 

In  lime  72  hours.  . 

422.0 

163.7 

63-1 

455 

1  68 

58.5 

I 

.08 

In  lime  96  hours-  - 

440.0 

I8I.7 

70-4 

475 

188 

65-5 

1.  08 

In  litne  120  hours. 

416.5 

158.2 

61.3 

449 

162 

56.5 

I 

.08 

In  lime  144  hours- 

429.0 

170.7 

66.1 

472 

185 

64-5 

I 

.10 

In  lime  168  hours- 

42I.O 

162.7 

63.0 

444 

157 

54-7 

I 

.08 

Unhaired     and 

fleshed   - 

236.8 

—  21-5 

-8.3 

256 

-3i 

—10.8    - 

-I 

.08 

CHANGES  IN  VOLUME,  WEIGHT  AND  DENSITY  OF 

FLANK. 

Number  II. 

Condition  of  the  skin 

Volume 
in  cc. 

Increase 
incc. 

Per  cent, 
increase 

Weight 
in  g. 

Increase 
ing. 

Per  cent, 
increase 

Density 

Drv  salted 

105-9 

—  122.2 

-53-5 

— 

— 

— 

— 

In  water  24  hours. 

221.  1 

—     7-0 

-  3-i 

— 

— 

— 

— 

In  water  48  hours. 

228.1 

0.0 

o.o 

252 

O.O 

O.O 

.11 

In  lime  24  hours-. 

324.0 

95-9 

42.0 

357 

105 

41.7 

.10 

In  lime  48  hours.  - 

359-5 

I3M 

574 

395 

143 

56.7 

.10 

In  lime  72  hours.  . 

375-0 

146.9 

64.4 

412 

160 

63.5 

.10 

In  lime  96  hours.- 

410.0 

181.9 

79-7 

43° 

178 

70.6 

.05 

In  lime  120  hours. 

432.0 

203.9 

89.4 

469 

217 

86.1 

.09 

In  lime  144  hours- 

395-0 

166.9 

73-i 

435 

183 

72.6 

.10 

In  lime  168  hours- 

369-5 

141.4 

62.0 

403 

151 

59-9 

•09 

Unhaired    and 

flpcViprl 

226.5 

—  1.6 

—  0.7 

245 

—7-0 

-2.8 

I 

.08 

CHANGES 

IN  VOLUME,  WEIGHT  AND  DENSITY  OF  BUTT. 

Number  III. 

Condition  of  the  skin 

Volume 
in  cc. 

Increase 
in  cc. 

Per  cent, 
increase 

Weight 
in  g. 

Increase 
ing. 

Per  cent, 
increase 

Density 

Drv  salted 

86.0 

—  III.7 

-56.5 

— 

— 

— 

111  water  24  hours. 

183.8 

-    13.9 

—  7.0 

— 

— 

— 

— 

In  water  48  hours- 

197-7 

O.O 

0.0 

2I9 

O.O 

O.O 

I 

.11 

In  lime  24  hours.. 

255-0 

57.3 

29.0 

284 

65 

29.7 

•  I 

.11 

In  lime  48  hours-  - 

292.0 

94-3 

47.6 

322 

103 

47.0 

I 

.10 

In  lime  72  hours.  . 

300.0 

102.3 

51.8 

334 

H5 

52.5 

I.  II 

In  lime  96  hours-  - 

318.0 

120.3 

60.9 

349 

130 

59.3 

1 

.10 

In  lime  120  hours. 

325.0 

127.3 

64.4 

357 

138 

63.0 

I 

.10 

In  lime  144  hours- 

327.5 

129.8 

65.7 

362 

'43 

65.5 

I 

.11 

In  lime  168  hours- 

296.0 

98.3 

49-7 

325 

1  06 

48.4 

I 

.10 

Unhaired    and 

fleshed  -  , 

'216.0 

18.7 

Q.1 

22? 

Tfi 

•7    7 

r 

r>n 

A   STUDY   OF   THE   CHANGES    IN    SKINS 

EXPERIMENT  39-6.— VOLUME. 
Per  cent,  increase  on  48-hour  soaked  volume. 


EXPERIMENT  39.— DENSITY. 


j/i 


/o? 


<0 

4" 


/O, 


A    STUDY   OF   THE    CHANGES   IN    SKINS 


33 


EXPERIMENT  39.— WEIGHT. 
Per  cent,  increase  on  48-hour  soaked  weight. 


:ntn:-::  :.:..   :.::: 


1C 


in 


Lime 


J}  ays 


EXPERIMENT  39.— VOLUME. 
Per  cent,  increase  on  48-hour  soaked  volume. 


34  A   STUDY   OF   THE   CHANGES   IN    SKINS 

ATTEMPTS  TO  PREVENT  THINNESS  OF  FLANK. 

In  looking  for  some  remedy  for  the  excessive  swelling  and  sub- 
sequent looseness  of  the  flank,  the  following  experiments  were 
made.  The  reasoning  was  that  the  flank  was  thinner  than  the 
rest  of  the  skin  and  hence  had  lost  more  inter-fibrillar  substance 
by  solution.  If  the  flank  could  be  protected  in  some  manner 
this  would  be  partially  prevented  and  the  resulting  leather  should 
not  have  so  thin  and  flabby  a  flank.  Some  substance  had  to  be 
used  which  was  easily  applied  and  relatively  pliable.  The  use  of 
aluminum  soap  was  suggested  and  it  was  tried.  The.  hides  were 
painted  with  a  hot  10  per  cent,  solution  of  aluminum  sulphate 
and  left  a  few  minutes.  Then  the  hides  were  painted  with  a  hot 
10  per  cent,  solution  of  ivory  soap.  The  pieces  were  then  limed 
in  the  usual  manner.  The  results  of  various  experiments  follow. 

Experiment  $-31. — Two  pieces  of  calfskin  which  had  been 
soaked  24  hours  in  water  were  painted  thickly  with  a  hot  10  per 
cent,  solution  of  aluminum  sulphate.  One  of  these  pieces  was 
immediately  placed  in  milk  of  lime,  the  other,  after  standing  10 
minutes,  was  painted  thickly  with  a  hot  10  per  cent,  solution  of 
ivory  soap.  A  third  piece  was  limed  24  hours,  washed  thoroughly 
in  water,  painted  with  a  hot  10  per  cent,  soap  solution  and  finally 
returned  to  the  limes.  All  three  pieces  gave  the  same  result  so 
far  as  could  be  detected  by  the  ordinary  methods  of  testing  the 
quality  of  leather.  The  hair  slipped  just  as  easily  as  in  the  ordi- 
nary cases  and  the  flank  was  neither  fuller  nor  firmer.  The 
results  were  negative. 

Experiment  $-34. — Two  pieces  of  calfskin  were  taken  after 
24  hours  soaking  in  water.  One  was  soaped  completely  three 
times  and  then  painted  three  times  with  an  aluminum  sulphate 
solution.  The  other  was  soaped  and  painted  once  on  the  flank 
only.  These  pieces  were  limed  as  usual  and  sent  to  the  tannery 
to  be  chrome  tanned  and  finished.  All  three  pieces  apparently 
gave  the  same  result.  No  appreciable  differences  were  noticed. 
The  hair  slipped  just  as  readily  as  though  the  pieces  had  been 
limed  in  the  ordinary  manner.  The  leather  appeared  to  have  a 
better  grain,  but  subsequent  tests  failed  to  confirm  this  conclusion. 

Experiment  $-35. — Eight  pieces,  which  had  been  soaked  24 
hours  in  water,  were  painted  and  soaped,  four  completely  and 


A   STUDY   OF   THE   CHANGES    IN    SKINS  35 

four  only  on  the  flank.  They  were  then  limed  and  tanned.  After 
tanning  the  tests  showed  negative  results.  It  was  impossible  to 
tell  by  inspection  the  soaped  from  the  unsoaped  area  nor  did  any 
of  the  pieces  differ  apparently  from  normally  limed  and  tanned 

skins. 

The  above  experiments  were  all  repeated  using  a  10  per  cent, 
soap  solution  only.  The  moment  the  hides  entered  the  limes  a 
lime  soap  was  formed.  The  results  of  these  experiments  were 
almost  identical  with  the  previous  ones. 

The  process  was  studied  more  quantitatively  in  Experiment 
8-36,  where  in  order  to  study  the  protective  action  of  soap  on 
various  parts  of  the  hide  a  dry  salted  calfskin  was  split  down 
the  backbone  into  two  pieces,  each  of  which  was  again  cut  at 
right  angles  to  the  backbone  into  three  portions.  The  pieces  on 
the  left  side  were  number  i,  2  and  3  starting  at  the  shoulder  and 
those  of  the  right  side,  4,  5  and  6  respectively.  The  object  was 
to  note  the  various  increases  in  volume  and  changes  in  structure 
occurring  in  the  process.  Sections  were  cut  parallel  to  and  at 
right  angles  to  the  backbone,  after  48  hours  soak,  after  96  hours 
liming  and  just  after  removing  from  the  limes.  The  pieces  were 
cut  in  each  case  from  a  piece  of  skin  taken  from  the  backbone 
edge  and  the  flank  edge  of  the  sample.  The  samples  were  sub- 
jected to  various  treatments  as  follows: 

No.  i. — Limed  168  hours  in  the  regular  manner. 

No.  2. — Limed  144  hours,  until  flank  unhaired  easily,  but  butt  not 

so  readily. 

No.  3. — Limed  196  hours,  2  days  over-limed. 
No.  4. — Soaped  (10  per  cent,  solution)  all  over  and  limed  normally 

168  hours. 

No.  5. — Soaped  flank  only  and  limed  normally  168  hours. 
No.  6. — Soaped  all  over  and  over-limed  2  days,  196  hours  in  all. 

The  sections  showed  that  the  flank  was  decidedly  of  a  looser 
structure  than  the  rest  of  the  skin.  The  loose  structure  was  noted 
in  the  very  beginning  of  the  process  and  the  soap  treatment 
apparently  failed  to  remedy  this  defect.  Even  if  the  lime  soap 
formed  should  hinder  further  action  of  the  lime,  it  could  not 
change  the  existing  loose  structure  into  a  compact  one.  The 


A   STUDY   OF   THE:   CHANGES   IN    SKINS 


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A   STUDY   OF   TH£   CHANGES   IN    SKINS 

EXPERIMENT  36.— VOLUME. 
Per  cent,  increase  on  48-hour  soaked  volume. 


EXPERIMENT  36.— VOLUME. 
Per  cent,  increase  on  48-hour  soaked  volume. 


A   STUDY   OF   THE)   CHANGES    IN    SKINS  39 

samples  were  all  unhaired,  fleshed,  bated,  pickled  and  chrome 
tanned  and  pronounced  fair  leather.  The  grain  in  all  samples 
was  good  and  showed  that  the  soap  treatment  caused  no  apparent 
harm.  The  volume  measurements  are  given  in  table,  Experiment 
SL36,  and  are  shown  also  in  curves. 

Some  attempts  were  made  to  fill  the  flank  so  that  it  would  be 
as  full  as  the  rest  of  the  skin.  The  hides  after  depilation  were 
suspended  in  i,  2,  5  and  10  per  cent,  solutions  of  glue  and  a 
few  cubic  centimeters  of  methylene  blue  were  added.  The  dye 
showed  the  extent  of  penetration  of  the  solution.  After  the  usual 
chrome  tannage,  the  results  obtained  were  unsatisfactory.  Some 
flanks  appeared  to  have  been  improved  and  others  were  as  if  they 
had  not  been  treated  with  glue.  Then  i,  2,  5  and  10  per  cent, 
gelatine  solutions  were  tried.  The  results  were  practically  the 
same  as  before.  In  both  cases  the  finishing  of  the  leather  was 
attended  by  difficulties.  Some  pieces  took  too  great  a  gloss  and 
others  remained  too  dull.  In  the  next  series  fresh  blood  and  glue, 
blood  and  gelatine  were  used.  About  50  per  cent,  of  blood  and 
50  per  cent,  of  a  10  per  cent,  solution  of  glue  or  gelatine  were 
used.  Although  great  care  was  taken  to  watch  the  hides  care- 
fully, many  were  destroyed  by  bacteria.  Even  the  addition  of 
germicides,  such  as  mercuric  chloride  and  phenol  failed  to  take 
care  of  the  putrefactive  bacteria.  So  long  as  bacterial  limes  are 
used  this  process  will  be  attended  with  very  great  difficulties  and 
can  hardly  be  made  commercial. 

Some  experiments  were  tried  on  pickled  stock  using  glue  and 
gelatine  to  fill  the  flanks.  The  results  did  not  justify  the  contin- 
uation of  work  along  these  lines. 

The  greatest  dfficulty  in  experiments  of  this  kind  is  that  the 
judgment  of  an  expert  is  required  to  determine  improvements. 
Moreover,  improvements  of  a  commercial  value  must  be  notice- 
able not  only  to  an  expert  but  also  to  the  layman. 

RESULTS  OF  STUDIES  OF  CHANGES  IN  WEIGHT,  VOLUME  AND 
AREA  OF  CALFSKIN  DURING  THE  TANNING  PROCESS. 

The  results  of  these  tests  can  best  be  studied  from  the  curves 
which  are  computed  to  a  common  basis  of  percentage  change 
from  the  condition  existing  when  the  skin  entered  the  limes. 


4O  A   STUDY   OF   THE   CHANGES   IN    SKINS 

Measurements  of  change  in  superficial  area  were  made  in  Experi- 
ments 26  and  28  and  are  given  in  detail  in  the  tables. 

The  dry  salted  skins  expanded  27.1  and  19.4  per  cent,  re- 
spectively in  area  during  the  soaking  process  but  both  remained 
relatively  constant  in  area  throughout  the  subsequent  operations 
of  liming,  bating  and  pickling.  No.  28  showed  a  considerable 
increase  after  unhairing  but  this  mechanical  stretching  disap- 
peared in  the  pickle.  Through  an  oversight  the  area  of  the  wet 
tanned  skin  was  not  determined  in  Experiment  26  and  the  area 
for  the  dried  finished  leather  while  about  5  per  cent,  greater  than 
that  of  the  dry  salted  skin,  has  little  significance  on  account  of 
the  impossibility  of  standardizing  the  amount  of  stretching  the 
leather  received  in  the  drying  process.  The  leather  of  8-28  meas- 
ured wet  showed  a  shrinkage  in  area  of  about  10  per  cent,  com- 
pared with  the  pickled  stock  and  an  increase  in  area  of  about  12 
per  cent,  compared  with  the  dry  skin. 

A  comparison  of  the  weight  and  volume  curves  of  all  experi- 
ments shows  great  general  similarity.  Both  volume  and  weight 
increase  in  approximately  the  same  ratio  during  the  soaking  and 
liming  process.  The  increase  is  rapid  during  the  first  24  hours 
in  water  and  slower  after  that  time.  On  putting  into  lime  the  in- 
crease is  again  very  rapid  during  the  first  24  hours  and  becomes 
slower  thereafter,  reaching  a  maximum  after  about  5  days  in  lime. 
These  limes  were  all  bacterial  but  did  not  contain  added  sulphides. 

The  increase  in  volume  of  different  pieces  varies  from  40  to 
80  per  cent.  The  experiments  on  changes  in  area  quoted  above 
show  that  very  little  change  took  place  after  the  skin  was  soaked. 
These  changes  in  volume  are  therefore  an  almost  direct  measure- 
ment of  changes  in  thickness.  This  increase  in  volume  and  hence 
approximately  of  thickness  runs  up  to  a  maximum  of  90  per  cent, 
over  that  of  the  soaked  hide.  The  least  total  increase  in  volume 
shown  by  any  skin  is  38  per  cent,  over  that  of  the  soaked  hide. 

Marked  differences  exist  between  different  portions  of  the 
same  skin  limed  in  the  same  solution.  In  each  Experiment  25, 
36  and  39  a  half  calfskin  was  trimmed  and  cut  at  right  angles  to 
the  backbone  into  three  pieces  of  approximately  equal  size.  These 
three  pieces  were  carried  through  the  whole  operation  together. 


A  STUDY  OF  THE;  CHANGES  IN  SKINS  41 

The  differences  in  the  maximum  amount  of  swelling  of  these 
three  skins  during  the  liming  process  is  as  follows  : 

Shoulder  Middle  Rump 

Per  cent.  Per  cent.  Per  cent. 

Experiment  25 51  40  62 

Experiment  36 72  80  88 

Experiment  39 70  90  65 

'No  conclusions  can  be  drawn  except  that  different  portions  of 
a  dry  salted  skin  may  swell  very  differently  in  the  limes.  This 
may  be  due  to  differences  in  thickness,  in  structure,  in  amount  of 
fat  or  to  other  causes  and  is  discussed  somewhat  later. 

While  the  curves  show  that  the  changes  in  volume  and  weight 
are  in  general  similar,  the  exact  relationship  is  shown  in  a  very 
similar  manner  by  the  curves  of  density.  Tests  25,  26,  27,  28  and 
39  are  available  for  a  study  of  this  relationship.  Any  errors  of 
measurement  are  magnified  in  this  method  of  treatment  and  as 
is  to  be  expected  the  curves  are  not  altogether  consistent.  Cer- 
tain general  features  are,  however,  clearly  recognizable.  The  den- 
sity decreases  on  soaking  in  water,  but  usually  increases  or 
stays  constant  during  the  first  24  hours  in  limes.  It  then  de- 
creases as  the  liming  process  proceeds  and  reaches  a  maximum 
after  96  hours  in  the  limes.  It  then  rises  to  a  distinct  maximum 
after  144  hours  in  lime  but  usually  falls  again  within  the  next 
day  or  two.  The  density  falls  again  in  the  bating  process 
whether  a  bran  drench  or  lactic  acid  be  used  and  rises  sharply 
in  the  pickle  to  fall  again  somewhat  in  the  wet  tanned  leather. 

The  changes  are  in  general  those  which  would  be  expected 
when  a  material  heavier  than  water  absorbs  water  and  swells. 
Ths  volume  increases  more  rapidly  than  the  weight.  The  same 
phenomenon  persists  in  the  limes.  The  sharp  change  in  the  curve 
while  still  in  the  limes  is  unexpected  but  may  be  in  some  way 
connected  with  bacterial  action.  The  immersion  in  the  feebly 
acid  bath  swells  the  hide  more  rapidly  than  the  weight  increases 
and  hence  the  density  falls  again.  The  pickle  shrinks  the  skin 
and  brings  its  density  back  to  a  figure  nearly  that  of  the  dry  skin. 

The  most  noticeable  defect  in  calfskins  is  the  flabbiness  of  the 
flank.  Microscopic  examination  showed  this  part  of  the  skin  to 
be  of  loose  structure  and  thinner  than  the  rest.  The  relative 
swelling  of  butt  and  flank  was  tested  in  Experiments  29,  33  and 


42  A   STUDY   OF   THE   CHANGES   IN    SKINS 

3QB.  In  every  case  the  flank  swelled  more  than  the  butt,  the 
figures  for  maximum  increase  in  volume  on  24  hours  soaking 
over  the  dry  volume  being: 

Butt  Flank 

Per  cent.  Per  cent. 

Experiment  33 25  45 

Experiment  396 61  86 

The  maximum  swelling  in  lime  referred  to  the  volume  after  soak- 
ing 48  hours  was: 

Butt  Flank 

s  Per  cent.  Per  cent. 

Experiment  29 63  92 

Experiment  396 60  71 

The  effect  of  coating  the  flesh  side  of  a  calfskin  with  lime  soap 
at  the  time  of  its  immersion  in  the  limes  is  shown  in  the  table 
and  the  two  sets  of  curves  in  Experiment  36.  The  soaped  pieces 
all  swelled  decidedly  more  than  the  unsoaped.  The  maximum 
swelling  expressed  in  percentage  increase  on  the  wet  volume  is 
as  follows: 

Not  soaped  Soaped 

Shoulder 38  72 

Middle 45  81 

Rump    68  88 

The  volumes  of  the  soaped  pieces  decrease  more  after  unhairing 
and  fleshing  than  do  those  of  the  unsoaped,  so  that  the  effect  of 
the  soap  seems  to  be  lost.  Volume  measurements  were  discon- 
tinued after  this  point  and  therefore  quantitative  figures  on  the 
finished  leather  are  not  available.  However,  the  pieces  which 
had  been  soaped  before  liming  seemed  slightly  fuller. 

STUDY  OF  DEPUTATION  IN  STERILE  LIMES — REVIEW  OF 
LITERATURE. 

Although  the  bacteria  of  bating  and  puering  have  been  studied 
quite  thoroughly,  those  of  the  limes  have  been  more  neglected. 
While  certain  agents  have  been  known  for  some  time,  which 
without  the  aid  of  bacteria,  were  able  to  depilate  a  hide,  still  in 
the  ordinary  processes  used  in  practice,  the  presence  of  bacteria 
was  not  only  taken  for  granted,  but  if  through  any  reason 
bacteria  were  absent  active  cultures  were  always  added.  This 
idea  has  had  so  firm  a  hold  that,  whenever  a  new  tannery  was 


A   STUDY   OF   THE   CHANGES   IN    SKINS  43 

established  some  old  lime  from  another  tannery  was  conveyed  to 
the  new  lime  pits  in  order  to  "start,"  that  is  inoculate  them. 

The  idea  that  a  solution  of  lime  could,  under  sterile  conditions, 
cause  loosening  of  the  hair  so  that  a  hide  could  be  unhaired  easily, 
was  considered  impracticable.  Parker13  states,  "Formerly  it  was 
believed  that  the  lime  swelled  the  fibers  of  the  hide,  dissolving 
the  hair  bulb  or  root  and  loosening  the  epidermis,  thus  rendering 
the  removal  of  the  hair  easy;  but  the  liming  process  is  now 
known  to  be  both  chemical  and  physical,  the  loosening  of  the  hair 
being  largely  due  to  the  action  of  enzymes  and  the  products  of 
bacteriological  action.  Hides  cannot  be  unhaired  by  sterile  limes, 
so  that  the  process  of  Payne  and  Pullman,14  by  which  the  hides 
were  first  soaked  in  caustic  soda  and  afterward  in  calcium 
chloride,  so  as  to  form  lime  within  the  fibers,  was  unworkable 
unless  preceded  by  the  soaking  of  the  hides  in  a  foul  soak  to  ob- 
tain the  necessary  bacteriological  action."  He  also  states,15  "It 
was  fully  realized  that  bacteriological  action  played  an  important 
part  in  the  unhairing  and  that  the  action  of  old  limes  was  largely 
bacterial  and  that  hides  could  not  be  unhaired  from  a  sterilized 
lime."  Procter10  believed  that  bacteria  were  essential  in  the  lim- 
ing process.  Stiasny17  states  that  the  liming  process  is  both  a 
chemical  and  bacteriological  one.  Villon  in  his  "Traite  de  la 
Fabrication  des  cuirs"  discusses  the  liming  and  sweating  proc- 
esses. He  states  positively18  "L/echauffe  est  une  fermentation 
particuliere  causee  par  un  microbe  determine.  L'epilage  a  la 
chaux  est  cause  par  la  meme  fermentation.  Que  la  peau  ne  se 
depile  pas  en  presence  de  la  chaux  apres  sterilization."  He  states 
that  the  unhairing  of  skins  is  due  to  the  action  of  definite  bacteria 
and  that  sterilized  lime  will  not  cause  unhairing  of  a  hide.  He 
sterilized  his  samples  of  hide  by  means  of  dry  heat.  He  sub- 
jected the  samples  to  50°  C.  for  24  hours  and  then  110°  C.  for 
10  minutes.  Schmitz-Dumont19  has  shown  that  not  all  the 
bacteria  present  were  killed  by  this  treatment. 
l*Jour.  Soc.  Chem.  Ind.  Vol.  29,  p.  (1912  910). 

14  English  patent,  No.  2,873. 

15  Jout .  Soc.  Chem.  Ind.  Vol.  31,  p.  371  (1912). 

16  Prin.  of  Leather  Mfg.  pp.  135,  137. 

17  Leather  Trades  Rev.  July  2,  1913. 

18  Villon  Traite  de  la  Fabrication  des  cuirs,  p.  487. 

19  Ding.  Polyt.Jour.  Vol.  300,  p.  140. 


44  A   STUDY   OF   THE   CHANGES   IN    SKINS 

Von  Schroeder20  made  many  experiments  along  the  above 
lines,  and  as  his  conclusions  are  different,  his  work  will  be  given 
more  fully.  His  methods  were  as  follows :  Hides  were  obtained 
from  a  tannery,  washed  3  days  in  water,  then  placed  in  a 
saturated  salt  solution.  The  salt  solution  was  changed  until  the 
hide  no  longer  absorbed  salt.  The  hides  were  kept  in  this  salt 
solution  and  were  considered  sterile.  The  lime  used  was 
sterilized  in  the  following  manner:  The  lime  solutions  were 
placed  in  flasks  around  the  neck  of  which  cotton  moistened  with 
salicylic  acid  had  been  wound  so  that  the  whole  could  be  covered 
with  a  Petri  dish.  These  flasks  were  placed  in  a  water  bath  up 
to  i  inch  from  the  top  of  the  neck  in  water.  The  bath  was  then 
heated  to  boiling  and  kept  boiling  y2  hour.  This  treatment  was 
repeated  on  3  successive  days.  This  lime  solution,  was  then 
called  sterile.  In  order  to  observe  the  action  of  sterile  water  on 
hides,  several  flasks  of  water  were  treated  precisely  like  the  lime 
solutions.  The  sterile  hides  were  placed  in  the  sterile  lime  and 
sterile  water  flasks  June  29th.  On  July  4th,  a  sample  was  taken 
from  a  water  and  a  lime  flask.  No  odor  was  perceptible  in  either 
case.  The  hair  could  be  removed  with  great  difficulty  and  in  fact 
it  was  almost  impossible  to  get  it  off.  One  cubic  centimeter  of 
the  water  and  one  of  the  lime  solution  were  now  transplanted  into 
10  cc.  of  gelatine.  All  these  sub-cultures  gave  a  positive  result, 
that  is  a  growth  of  bacteria  or  molds,  whereas  if  the  solution  had 
been  really  sterih  there  should  have  been  no  growths.  On  July 
nth  a  flask  of  each  kind  was  again  opened.  The  hair  slipped 
easily.  Again  all  sub-cultures  made  gave  positive  results.  On 
August  3rd  the  remaining  flasks  were  opened  and  all  sub-cultures 
again  gave  positive  results.  Moreover,  the  solutions  all  had  a 
putrid  odor. 

Van  Schroeder  then  took  part  of  the  water  in  the  flasks,  added 
it  to  some  sterile  limes  and  the  sub-cultures  made  showed  few 
colonies.  His  conclusion  was  that  the  lime  killed  the  bacteria 
contained  in  the  water.  His  final  conclusion  based  on  this  last 
experiment  was  that  in  the  limes,  unhairing  takes  place  without 
bacterial  action  in  a  short  time,  but  that  in  pure  (reinem)  water 
only  after  bacteria  have  developed  and  produced  ammonia 
enough  to  make  the  solution  alkaline.  His  second  series  was  as 
20  Ding.  Poly  t.  Jour.  Vol.  301,  pp.  65,  90. 


I 

A    STUDY   OF   THE    CHANGES   IN    SKINS  45 

follows:  The  hides  from  the  saturated  salt  solution  were  placed 
in  99  per  cent,  alcohol  which  was  renewed  every  day  for  4  days. 
These  hides  were  considered  sterile.  The  flasks  containing  water 
and  lime  water  solutions  were  sterilized  as  before.  All  except 
one  of  the  sub-cultures  taken  after  4  days  gave  positive  results. 
In  this  case  some  hairs  were  transplanted  to  gelatine  by  means 
of  a  forceps  sterilized  in  a  flame.  There  is  a  possibility  that  the 
forceps  was  too  hot  and  killed  the  bacteria,  or  that  the  melted 
gelatine  was  too  warm.  After  6  days  two  more  flasks  were 
opened  and  sub-cultures  made.  All  but  two  gave  positive  re- 
sults. These  two  sub-cultures  were  made  by  transplanting  o.i  cc. 
and  o.oi  cc.  of  the  lime  solution  in  10  cc.  of  gelatine.  The  final 
conclusion  drawn  from  these  experiments  was  that  "Die  Vor- 
bereitung  cler  Haut  zum  Enthaaren  durch  den  Aescher  process 
von  Bakterien  iiberhaupt  unabhangig  und  nur  eine  Wirkung  der 
alkalischen  Reaction  des  Kalkes  ist."  Von  Schroeder  then  as- 
sumes that  Villon's  idea  that  bacillus  pilline  must  be  present  in 
limes  in  order  that  the  hair  be  loosened,  is  no  longer  true.  Un- 
fortunately Von  Schroeder  died  before  the  work  was  completed 
and  the  paper  was  published  by  others.  The  results  do  not  bear 
out  the  assumption  that  the  hides  and  solution  used  were  really 
sterile.  On  the  contrary  all  but  two  sub-cultures  from  the  sup- 
posedly sterile  solutions  gave  positive  results.  The  sub-cultures 
which  were  negative  under  aerobic  condtions  were  not  duplicated 
under  anaerobic  conditions.  There  is  no  valid  reason  why  an- 
aerobic bacteria  could  not  have  been  present.  He  also  neglected 
to  guard  against  the  inhibiting  action  of  the  lime.  He  showed  at 
great  length  that  the  lime  solution  killed,  or  rather  to  be  accurate 
inhibited  the  growth  of  bacteria  obtained  from  the  infected  water 
used  in  the  first  experiment.  Afterward  he  did  not  take  this  fact 
into  consideration,  but  transplanted  his  solution  from  the  lime 
flasks  into  the  same  amount  of  gelatine — 10  cc.  as  in  the  experi- 
ment using  water  only. 

Griffith21  made  several  experiments  on  a  sterile  liming  process 
using  carbon  bisulphide  and  phenol  as  disinfectants.  He  does  not 
give  any  data  nor  information  about  the  actual  methods  used  or 
precautions  taken  to  prevent  infection  of  the  solutions  but  merely 
speaks  of  "pieces  of  hide  previously  sterilized  with  carbon  bisul- 
21  JOURNAI,  Amer.  Leather  Chem.  Asso.,Vol  5,  p. 115  (1910). 


46  A  STUDY  OF  THE;  CHANGES  IN  SKINS 

phide  and  with  phenol  and  the  liming  carried  out  in  sealed  jars. 
The  carbon  bisulphide  hide  unhaired  in  24  days  and  the  phenol 
hide  unhaired  in  18  days  and  an  experienced  bacteriologist  was 
unable  to  discover  the  presence  of  bacteria.  Von  Schroeder  ex- 
perimented with  fresh  salted  hides  under  sterile  conditions  and 
he  was  unable  to  discover  that  the  absence  of  bacteria  influenced 
the  activity  of  the  lime  as  a  depilatory."  The  above  statements 
would  have  been  more  convincing  if  the  methods  of  bacterio- 
logical control  had  been  given  more  fully.  Griffith  concedes  that 
Von  Schroeder's  work  was  correct  and  he  admits  that  the  latter 
worked  under  sterile  conditions.  As  was  pointed  out  before  this 
was  not  the  case.  Von  Schroeder  never  had  sterile  conditions 
prevailing  in  any  of  his  experiments  as  his  sub-cultures  always 
showed  bacteria  or  molds.  Griffith  relied  entirely  on  carbon 
bisulphide  as  a  sterilizing  agent.  Carbon  bisulphide  may  be  an 
antiseptic  agent  but  it  is  not  a  disinfectant  for  it  does  not  kill  all 
organisms,  as  was  shown  by  Procter.22 

The  experiment  with  carbon  bisulphide  gave  approximately 
the  same  results  as  that  with  phenol.  This  may  have  been  due  to 
the  fact  that  under  the  conditions  existing  during  the  experiment 
the  carbon  bisulphide  was  present  in  sufficient  quantity  to  pre- 
vent a  noticeable  increase  in  the  number  of  bacteria  present.  The 
above  experiments  cannot  be  accepted  as  accurate  in  the  scientific 
sense. 

EXPERIMENTAL  WORK  ON  STERILIZATION  OF  HIDES. 

The  following  experiments  were  planned  to  settle  definitely 
whether  bacteria  were  necessary  in  the  depilation  process.  The 
sterilization  of  hides  offered  the  first  difficulty.  After  reading 
of  various  methods23  using  sulphur  dioxide,  phenol,  etc.,  the 
Seymour- Jones  method  was  finally  adopted  as  offering  the  best 
chances  of  success.  The  method  consists  of  immersion  of  the 
hide  for  24  hours  in  a  0.02  per  cent,  solution  of  mercuric  chloride 
and  a  0.5  per  cent,  solution  of  formic  acid. 

In  order  to  test  Seymour-Jones  method  of  sterilization  for  its 
effectiveness  as  a  sterilizing  agent  the  following  experiments  were 
made.  Samples  of  hide  about  1x2  centimeters  were  soaked  in 

22  Procter,  Principles  of  Leather  Manufacture,  p.  135. 

23  JOURNAI,  Amer.  Leather  Chem.  Asso.,  Vol  5,  pp.  508-10. 


A  STUDY  OF  THE;  CHANGES  IN  SKINS  47 

the  solution  24  hours.  They  were  then  removed  with  sterile  for- 
ceps and  washed  three  times  by  immersion,  using  a  liter  of 
sterile  water  each  time.  Then  they  were  planted  by  means  of 
sterile  forceps  into  150  cc.  of  sterile  medium,  beef  tea,  gelatine, 
agar,  pea-bean  medium,  and  litmus  glucose  gelatine  being  used. 
The  results  are  shown  in  the  table. 

SEYMOUR-JONES  TEST. 

Anaerobic 
conditions. 

in  a 

Novy  jar,  over 

hydrogen.  i,it-    Check  for  Check 

mus  glucose     Anaerobes          Aerobes 
No.    Beef  tea   Gelatine  Pea-bean      Agar  gelatine         B.  tetanus          B.  lactici 

I....    -  +  +  +  +  + 

2-...     - 


Although  these  solutions  all  showed  negative  results  it  is  neces- 
sary, before  admitting  the  test  to  be  conclusive,  to  show  that  the 
amount  of  mercuric  chloride  transferred  could  not  have  been 
sufficient  to  have  inhibited  the  growth  of  bacteria  in  the  culture 
media.  Mercuric  chloride  acts  as  an  antiseptic  agent  even  in 
dilutions  of  I  to  100,000.  The  samples  after  washing  thoroughly 
in  3  liters  of  sterile  water  had  very  little  mercuric  chloride  ad- 
hering. Moreover,  the  volume  of  medium  used  was  large,  1500:. 
or  more  in  all  cases.  This  again  increases  the  dilution  of  the 
mercuric  chloride  and  hence  eliminates  its  antiseptic  action. 

The  dilution  at  which  formic  acid  still  exerts  its  antiseptic 
action  is  not  known  definitely.  The  fact  was  taken  into  consid- 
eration, however,  that  the  antiseptic  action  of  formic  acid  is 
usually  less  than  that  of  mercuric  chloride.  If  one  assumes  the 
piece  of  hide  transferred,  to  be  all  formic  acid,  and  then  takes 
into  consideration  the  dilution  resulting  from  the  washing  in 
sterile  water,  one  will  see  that  the  dilution  is  more  than  I  to 
200,000  and  that  there  is  no  chance  of  any  antiseptic  action  inter- 
fering with  the  results.  In  order  to  check  whether  the  medium 
was  suitable  for  growing  bacteria,  bacillus  tetanus  and  bacillus 
acidi  lactici  were  planted  under  anaerobic  and  aerobic  conditions 
respectively.  The  results  were  positive  in  all  cases. 

Since  the  checks  were  always  positive  and  the  sub-cultures 


48  A   STUDY   OF   THE    CHANGES   IN   SKINS 

from  the  sterilized  hides  negative,  it  was  therefore  considered 
proven  that  the  Seymour-Jones  method  of  sterilization  is  ef- 
fective under  the  given  conditions  of  experiment. 

TEST  FOR  BACTERIA  IN  THE  LIMES. 

Since  there  might  be  some  question  as  to  the  presence  of 
bacteria  in  the  limes,  sub-cultures  were  made  on  agar,  beef  tea, 
pea-bean  media  and  gelatine.  All  sub-cultures  gave  positive  re- 
sults. 

Wood24  has  shown  that  bacteria  of  various  kinds  are  present 
in  the  limes.  Abt25  has  also  proven  that  bacteria  are  present  in 
the  liming  process. 

The  medium  used  in  transplanting  sub-cultures  in  all  the  fol- 
lowing experiments  was  slightly  more  alkaline  than  that  usually 
employed  for  this  purpose. 

EXPERIMENTAL  WORK — LABORATORY  TESTS  ON  DEPUTATION. 

The  procedure  now  used  was  as  follows:  A  250  cc.  Soxhlet 
flask,  provided  with  a  tight  cotton  plug  was  sterilized  for  I  minute 
at  200°  C.  in  a  dry  heat  sterilizer.  It  was  cooled  and  175  cc.  of 
water  and  50  grams  of  slaked  lime  were  added.  The  flask  was 
then  autoclaved  at  110°  C.  for  20  minutes  and  allowed  to  cool. 
A  piece  of  hide  which  had  been  previously  sterilized  in  a  solu- 
tion (Seymour- Jones)  of  1-5,000  mercuric  chloride  and  0.5  per 
cent,  formic  acid,  for  24  hours,  was  added  to  this  solution  by 
means  of  sterile  forceps.  This  flask  was  then  examined  every 
2  or  3  days,  great  care  being  taken  to  prevent  infection  of  its  con- 
tents. After  ii  days  the  hair  could  be  removed  with  difficulty, 
but  after  13  days  the  hide  could  be  easily  unhaired. 

In  order  to  prove  conclusively  that  bacteria  were  absent,  sub- 
cultures of  the  lime  solution  and  of  hair  were  made  on  various 
media  under  aerobic  and  anaerobic  conditions.  That  the  med- 
ium used  was  suitable  for  the  growth  of  bacteria  was  proven  by 
planting  test  organisms.  For  this  purpose  bacillus  acidi  lactici 
and  bacillus  tetanus  were  used  under  aerobic  and  anaerobic  con- 
ditions, respectively.  The  results  obtained  are  shown  in  the  fol- 
lowing table : 

24y.  Soc.  Chem.  Ind.,  Vol.  29,  p.  666.  (1910). 

25  Bull.  Syndicat.  Gen.  Cuirs  et  Peaux,  p.  416,  Nov.  10,  1908. 


A   STUDY   OF   THE    CHANGES   IN   SKINS  49 

CHECK  TEST  ON  STERILITY  OF  CONDITIONS. 

Under  anaerobic  conditions 
in  a  Novy  jar  previously 
exhausted  and  hydrogen 

passed  in. 
Beef  tea        Gelatine        Pea-bean        I^itmus  glucose  gelatine 

i  loop  of  lime  solution  .  — 

Hair - 

Checks    -f  +  +  + 

These  results  are  very  satisfactory  and  show,  since  all  the  sub- 
cultures were  negative  and  the  checks  positive,  that  no  bacteria 
capable  of  growing  were  present  in  the  limes  used. 

After  it  had  been  shown  that  the  Seymour- Jones  method  of 
sterilization  with  mercuric  chloride  and  formic  acid  was  reliable 
and  preliminary  tests  had  shown  that  it  was  possible  to  unhair 
a  skin  with  sterile  limes,  the  following  series  of  tests  was  under- 
taken to  study  the  process  more  quantitatively.  Four  different 
solutions  were  used  to  determine  how  lime  alone,  and  lime  with 
sulphur  compounds  acted.  One  flask  contained  lime  only,  a  sec- 
ond lime  and  red  arsenic  sulphide,  a  third,  lime,  red  arsenic  sul- 
phide and  hair,  and  the  fourth  lime  and  hair.  The  solutions  con- 
taining hair  were  boiled  vigorously  for  45  minutes,  before  use, 
with  the  idea  that  some  hydrolysis  of  the  hair  would  take  place 
with  formation  of  soluble  sulphur  compounds  and  amino  acids 
and  that  thus  the  action  of  an  old  lime  might  be  simulated.  The 
details  of  the  tests  are  as  follows : 

Four  pieces  of  dried  calfskin  2x3  inches  in  area  were  soaked 
24  hours  in  a  solution  of  0.02  per  cent,  mercuric  chloride  and 
0.5  per  cent,  formic  acid.  Four  250  cc.  Soxhlet  flasks  were 
plugged  with  cotton  and  sterilized  for  i  minute  at  200°  C.  in  a 
dry  heat  sterilizer.  To  one  of  these  flasks  50  grams  of  lime  and 
175-200  cc.  of  water  were  added.  To  another  sterile  flask  50 
grams  of  lime,  175-200  cc.  of  water  and  1.5  grams  of  red  arsenic 
sulphide  were  added.  Then  the  flasks  which  were  to  contain 
boiled  hair  were  prepared  as  follows :  200  cc.  of  water,  50  grams 
of  lime  and  10-12  grams  of  hair  clipped  from  a  calfskin,  were 
boiled  vigorously  for  45  minutes.  This  solution  was  placed  in 
a  sterile  flask.  Then  200  cc.  of  water,  50  grams  of  lime,  1.5  grams 
of  red  arsenic  sulphide  and  10-12  grams  of  hair  were  boiled  45 
minutes  and  put  into  the  fourth  sterile  flask.  Then  the  four 
flasks  were  autoclaved  for  20  minutes  at  110°  C.  A  piece  of 


A   STUDY   OF   THE   CHANGES   IN   SKINS 


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A   STUDY   OF   THE    CHANGES   IN   SKINS  51 

sterile  hide  was  now  planted  in  each  of  the  flasks  after  cooling, 
by  means  of  sterile  forceps. 

The  following  table  gives  some  of  the  observations  made  on 
these  samples.  Every  time  the  hides  were  examined  great  care 
was  taken  to  handle  them  with  sterile  instruments  and  in  such  a 
manner  that  they  remained  sterile.  The  flasks  were  all  kept  at 
the  room  temperature.  They  were  not  examined  every  day,  for 
the  danger  of  contamination  would  have  increased  at  a  greater 
rate  than  the  notable  differences  in  the  skin.  The  remarks  con- 
cerning the  condition  of  the  skin  are  rather  indefinite  to  be  sure, 
but  the  changes  were  very  gradual  and  consisted  in  the  main  in 
such  as  are  hard  to  describe  accurately. 

In  order  that  there  might  be  no  question  of  the  sterility  of  the 
various  flasks,  sub-cultures  were  made  on  various  media  after 
the  test  had  been  running  2  months.  Gelatine,  beef  tea  and 
pea-bean  media  were  used  for  aerobic  and  litmus  glucose  gelatine 
for  anaerobic  experiments.  B.  acidi  lactici  and  B.  tetanus  were 
used  as  checks  respectively.  The  results  follow  in  the  table. 
EXPERIMENT  38.— CHECK  ON  STERILITY  OF  SOLUTIONS. 

Number  of  flask  I  II          III          IV 

Gelatine  plates —        —        —  Planted  2-12-14 

Gelatine  tubes -  4*  Examined  daily  from 

Pea-bean  tubes —  —     2-12102-24 

Beef  tea  tubes - 

Checks 4         +         4         4 

Anaerobic  conditions  in 
Novy  jar  over  hydrogen  •  •  — 

Litmus  glucose  gelatine Planted  2-12-14 

Checks    -|-         4         4         4     Examined  2-26-14 

*  One  positive  result  out  of  eight  gelatine  tubes. 

It  will  be  noted  that  all  the  results  are  negative  with  the  ex- 
ception of  one  of  the  eight  gelatine  tubes  planted  from  Flask  II. 
To  study  this  organism  further  it  was  transplanted  and  plated. 
It  proved  to  be  a  streptococcus,  white,  liquefying  gelatine  and 
was  probably  Matschek's  white  streptococcus.  Then  six  more 
gelatine  sub-cultures  were  made  from  the  original  flask.  All 
were  negative.  Therefore,  it  is  reasonable  to  presume  that  this 
one  tube  became  infected  through  air  and  technique.  The 
anaerobes  were  transplanted  to  litmus  glucose  gelatine  and 
placed  in  a  Novy  jar.  This  was  exhausted  to  28.8  millimeters 
vacuum,  then  hydrogen  was  passed  in.  This  process  was  repeated 
three  times  then  the  jar  was  closed  and  left  for  14  days.  No 


52  A   STUDY   OF   THE)    CHANGES   IN    SKINS 

growths  were  noticeable.  Tetanus  bacillus  was  used  as  a  check 
and  gave  a  good  growth  in  litmus  glucose  gelatine  to  which  one 
loopful  of  sterile  lime  water  had  been  added.  In  the  case  of 
aerobes,  the  check  used  on  gelatine  with  one  loopful  of  sterile 
lime  was  bacillus  acidi  lactici.  In  all  cases  the  effect  of  the  lime 
and  water  which  was  unavoidably  conveyed  by  the  platinum  loop 
during  inoculation,  and  which  might  have  had  an  antiseptic  or 
germicidal  action,  was  provided  for  by  using  a  large  amount  of 
medium  at  least  15  cc.  in  each  case  and  to  be  more  certain,  for 
each  set  one  flask  containing  100-150  cc.  of  medium  was  used. 

This  Experiment  38  was  continued  5  months  as  shown  by  the 
table  and  at  the  end  of  the  period,  the  flasks  were  again  tested. 
All  tubes  and  flasks  showed  negative  results,  that  is  no  growths. 
The  checks  were  all  positive  showing  that  conditions  were  fav- 
orable for  the  growth  of  bacteria.  Details  are  given  in  the  fol- 
lowing table: 

EXPERIMENT  38. — FINAL  CHECK  ON  STERILITY  OF  SOLUTIONS. 

Number  of  flask  I  II          III         IV 

Planted  3-8-14  examined 

Gelatine  plates -  daily  from 

Gelatine  tubes —  —    3-9  to  3-23 

Pea-bean — 

Beef  tea - 

Checks -h        +         -f         + 

Anaerobic    conditions  L/it-  Planted  3-8-14 

mus  glucose  gelatine —  —     Examined  after  14  days 

Check +         +        +        + 

EXPERIMENT  40. 

This  experiment  was  made  both  to  check  results  of  the  previous 
one  and  to  see  whether  the  presence  of  hair  had  any  marked  ef- 
fect on  the  changes  taking  place  during  the  sterile  liming.  The 
samples  of  hide  were  sterilized  24  hours  in  Seymour- Jones  solu- 
tion then  transferred  with  sterile  forceps  to  sterile  flasks  con- 
taining lime,  and  lime  and  arsenic  sulphide.  The  samples  were  in 
one  case  hide  which  had  had  the  hair  closely  clipped  off  before 
sterilization  and  in  the  other  case  normal  hides  with  hair  on.  At 
the  same  time  20  grams  of  hair  were  sterilized  3  days  and  then 
placed  in  600  cc.  of  water  containing  50  grams  of  lime  with  the 
idea  in  mind  of  noting  changes  on  pure  hair  under  said  conditions. 
The  results  follow  in  the  table.  Sub-cultures  were  made  from 
all  flasks  on  various  media  precisely  as  in  the  previous  tests.  The 
results  were  all  negative  and  are  shown  in  the  following  tables : 


A    STUDY   OF   THE:    CHANGES   IN    SKINS 


53 


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A   STUDY   OF   THE    CHANGES   IN   SKINS  55 

EXPERIMENT  40. — CHECK  ON  STERLITY  OF  SOLUTIONS 
AFTER  TEN  WEEKS. 

Number  of  flask  I  II          III         IV 

Gelatine  plates -  —  Planted  2-12  examined 

Gelatine  tubes -  -  Daily  from  2-12  to  2-24 

Beef  tea  tubes - 

Pea-bean  tubes — 

Checks +         4-         +         + 

Anaerobic  conditions.  Lit- 
mus glucose  gelatine  in  Planted  2-12  examined 
Novy  jar  over  hydrogen  —  2-26 

Checks  -f        +         4-        4- 

EXPERIMENT  40.— FINAL  CHECK  ON  STERILITY  OF  SOLUTIONS. 

Number  of  flask  I  II          III          IV 

Gelatine  plates -  -  Planted  3-9  examined 

Gelatine  tubes -  -  Daily  after  3-10  to  3-20 

Beef  tea  tubes - 

Pea-bean  tubes - 

Checks   4-         +         4-         4- 

Anaerobic  conditions  on  lit- 
mus glucose  in   a   Novy  Planted  3-9 
jar  over  hydrogen   -                                   -  Examined  3-23 

Checks 4-         +         +         + 

EXPERIMENTS  41. 

As  a  final  check  on  the  previous  results  the  following  tests 
were  made :  Two  flasks  were  plugged  with  cotton,  sterilized  by 
dry  heat  for  I  minute  at  200°  C.  To  each  flask  100  cc.  of  water 
and  10  grams  of  lime  were  added.  They  were  then  autoclaved  20 
minutes  at  110°  C.  Two  pieces  of  calfskin  I  x  2  inches  were 
sterilized  48  hours  in  a  Seymour-Jones  solution.  The  sterile 
hides  were  placed  in  the  flask  October  30,  1913.  The  flasks  were 
left  undisturbed  at  room  temperature  until  March  9,  1914,  when 
they  were  opened  and  sub-cultures  made  as  in  previous  experi- 
ments. All  sub-cultures  were  negative  but  the  checks  were  posi- 
tive. The  flask,  therefore,  contained  a  sterile  solution. 

The  skin  had  changed  considerably  in  its  4  months  treatment 
in  sterile  lime.  The  hair  was  all  very  loose;  the  upper  layer  and 
the  flesh  side  of  the  skin  had  become  mushy  and  swollen.  The 
corium  was  fairly  firm  but  glassy  in  appearance.  No  odor  was 
noticeable.  The  preceding  experiments  had  all  been  made  on 
calfskin.  In  order  to  check  the  results  on  heavier  hides  a  sample 
of  sterilized  cowhide  was  placed  in  a  sterile  lime  solution  Decem- 


56  A   STUDY   OF   THE    CHANGES   IN   SKINS 

her  12,  1913.  This  contained  5  grams  of  lime  and  0,5  gram  of 
sodium  sulphide  in  100  cc.  of  water.  The  hide  was  examined 
March  9,  1914.  The  flask  had  been  left  undisturbed  during  this 
time.  Sub-cultures  were  made  as  before,  and  all  results  were 
negative.  This  showed  that  the  solution  was  sterile. 

This  hide  had  also  changed  materially  by  its  3  months'  treat- 
ment in  sterile  lime.  All  the  hair  was  dissolved.  The  upper  layer 
had  been  dissolved  and  the  flesh  side  had  not  only  become  mushy 
as  in  the  previous  experiment,  but  in  fact  it  had  disappeared, 
leaving  only  a  firm  tough  layer  of  corium,  which  had  apparently 
suffered  very  little  change. 

DEPUTATION  IN  STERILE  SOLUTION  AND  SUBSEQUENT 
TANNAGE. 

After  these  preliminary  tests  of  liming  under  sterile  conditions, 
somewhat  larger  pieces  of  hide  were  used  and  carried  through 
the  entire  tanning  process.  The  final  products  were  then  com- 
pared with  commercial  products  obtained  by  liming  in  the  usual 
manner. 

The  first  experiments  were  on  pieces  of  cowhide  which  were 
tanned  subsequently,  through  the  courtesy  of  Mr.  V.  A.  Wallin, 
in  the  Wallin  tanneries  at  Grand  Rapids. 

EXPERIMENT  42.     EXPERIMENTS  ON  COWHIDES. 

Two  pieces  of  cowhide  about  i  x  10  feet  were  sterilized  3 
days  in  Seymour-Jones's  solution.  The  bottles  in  which  the 
previous  solutions  had  been  sterilized  had  been  made  of  cheap 
cast  glass  but  had  caused  much  trouble  by  breaking  during  ster- 
ilization, in  spite  of  the  utmost  precautions  taken  while  heating 
and  cooling  them.  This  difficulty  was  overcome  by  using  narrow 
and  deep  galvanized  iron  cans  5  centimeters  by  42  centimeters  by 
46  centimeters.  Small  shelves  were  arranged  so  the  hides  could 
be  suspended  over  glass  rods.  The  solutions  to  be  used  were  ster- 
ilized in  these  cans  by  boiling  over  a  direct  flame  for  4  to  8  hours. 
The  cover,  not  fitting  tightly,  allowed  a  cloth  moistened  with  0.02 
per  cent,  mercuric  chloride  solution  to  be  placed  over  the  can  in 
such  a  manner  that  it  could  be  kept  sterile. 

Hide  No.  i,  was  limed  in  a  solution  containing  5  grams  of 
lime  and  0.5  gram  of  sodium  sulphide  crystals,  in  400  cc.  of 


A   STUDY   OF   THE    CHANGES   IN   SKINS  57 

water,  for  3  days.  It  was  removed  while  slightly  underlimed  and 
placed  in  a  can  containing  a  sterile  saturated  lime  solution  and 
shipped  to  the  Wallin  Tannery,  Grand  Rapids,  Michigan,  to  be 
put  through  their  regular  tanning  process. 

Hide  No.  2,  was  limed  in  the  same  kind  of  a  solution  as  No.  I 
but  for  6  days.  It  was  removed  and  shipped  in  a  sterile  saturated 
lime  solution.  Sub-cultures  made  as  in  previous  experiments 
gave  negative  results  and  showed  that  these  hides  had  been  un- 
haired  in  sterile  solution. 

The  finished  sample  of  leather  from  hide  No.  I  was  returned 
from  the  tannery  with  the  comment: 

"The  job  seems  to  be  satisfactory.  The  stock  is  a  little  bit 
snappy  on  the  grain  but  it  is  not  certain  that  this  has  any  rela- 
tion to  the  liming." 

The  finished  sample  of  leather  from  hide  No.  2  has  not  yet 
been  returned  from  the  tannery. 

EXPERIMENT  8-43. 

Two  pieces  of  cowhide  were  received  wet  and  salted.  They 
were  washed  thoroughly  in  water  and  sterilized  in  Seymour-Jones 
solution  for  48  hours.  The  limes  used  were  made  up  by  dissolv- 
ing 5  grams  of  lime  and  0.5  gram  of  sodium  sulphide  in  400  cc. 
of  water.  They  were  sterilized  by  boiling  4  to  8  hours  over  a 
free  flame.  The  hides  were  now  treated  as  follows :  One  piece 
was  limed  4  days,  then  placed  in  a  sterile  saturated  lime  solution 
and  shipped  to  the  tannery.  The  other  piece  was  purposely  over- 
limed  and  after  7  days  in  the  lime  was  sent  to  the  tannery  in  the 
same  way  as  was  the  other  piece.  Sub-cultures  from  the  limes 
used,  were  made  on  various  media  in  the  same  manner  as  in 
previous  experiments.  All  sub-cultures  were  negative  and 
showed  that  the  solutions  had  been  sterile. 

The  loss  of  hide  substance  in  the  liming  process  is  often  con- 
siderable and  an  examination  was  made  of  some  of  these  lime 
solutions  to  determine  the  amount  of  hide  substance  dissolved. 
For  comparison  an  old  lime  from  the  Wallin  tannery  was  also 
tested.  The  hide  substance  in  solution  was  calculated  from  the 
content  of  ammonia  shown  by  the  Kjeldahl  method.  The  results 
are  shown  in  the  following  table : 


5§  A   STUDY   OF   THE   CHANGES    IN   SKINS 

HIDE  SUBSTANCE  DISSOLVED  IN  LIMES. 

Ammonia         Hide  substance 
Source  of  lime  g.  per  1.  g.  per  1.  Remarks 

Experiment  42  0.1366  0.623  Hide  3  days  in 

Hide#i. 0.1326  sterile  lime. 

Experiment  42 0.3145  1-457  Hide  6  days  in 

Hide  #2. 0.3155  sterile  lime. 

Experiment  43 0.41 14  1.909  Hide  4  days  in 

Hide  #i. 0.4138  sterile  lime. 

Experiment  43 0.9479  4.376  Hide  7  days  in 

Hide  #2. 0.9452  sterile  lime. 

Old  lime  from  Wallin  tan 1-439  6.694 

1-454 

The  amount  of  hide  substance  dissolved  by  these  sterile  limes 
is  less  than  that  shown  in  the  old  lime  from  the  tannery  but  not 
enough  is  known  of  the  changes  of  limes  with  continued  use  to 
warrant  a  positive  conclusion. 

EXPERIMENTS  ON  CALFSKINS. 

Calfskins  received  in  the  dry  salted  state  were  unhaired  in 
sterile  limes  and  through  the  courtesy  of  Mr.  Carl  E.  Schmidt, 
tanned  by  the  chrome  process  in  his  Detroit  tannery. 

Considerable  difficulty  had  been  experienced  in  handling  the 
can  used  to  contain  the  sterile  limes  in  the  previous  experiments, 
and  spots  appeared  on  the  hides  where  they  touched  the  metal. 
The  calfskins  were  limp  enough  so  that  glass  vessels  could  be 
used. 

EXPERIMENT  S-4iA. 

A  bottle  of  about  6  liters  capacity  was  plugged  with  cotton  and 
sterilized  at  200°  C.  for  i  minute  in  a  dry  heat  sterilized.  One- 
half  of  a  small  calfskin,  weighing  250  grams  was  sterilized  24 
hours  in  a  Seymour-Jones  solution.  A  lime  solution  containing 
5  grams  of  lime  and  0.15  gram  of  red  arsenic  sulphide  in  400  cc. 
of  water  was  put  into  the  sterile  bottle  and  this  was  autoclaved 
at  110°  C.  for  20  minutes.  The  sterile  skin  was  now  placed  in 
the  sterile  lime  and  left  for  9  days.  The  hair  slipped  very  easily. 
This  skin  was  sent  to  the  Carl  E.  Schmidt  Tannery  at  Detroit, 
Michigan,  where  it  was  chrome  tanned  and  finished.  The  product 
was  of  little  value.  The  grain  could  be  peeled  off  easily.  The 
leather  had  very  little  strength  and  felt  very  thin.  The  liming 
had  been  allowed  to  proceed  too  long  and  the  skin  had  become 
seriously  damaged.  The  grain  was  also  drawn  and  harsh. 


A   STUDY   OF   THE)   CHANGES   IN    SKINS  59 

In  subsequent  tests  on  calfskin  a  large  Jena  flask  of  about  15 
liters  capacity  was  plugged  with  sterile  cotton.  The  flask  was  too 
large  to  permit  sterilization  in  a  dry  heat  sterilizer  hence  it  was 
only  washed  with  distilled  water.  The  cotton  plug,  after  it  was 
made  to  fit  the  flask  was  sterilized  for  5  minutes  at  200°  C.  A 
lime  solution  was  made  containing  5  grams  of  lime  and  0.15  gram 
of  red  arsenic  sulphide  per  400  cc.  of  water,  and  put  into  the 
flask.  This  was  then  autoclaved  4  to  5  hours  at  110°  to  120°  C. 

EXPERIMENT  44. 

One-half  of  a  small  calfskin  was  sterilized  48  hours  in  Sey- 
mour-Jones's solution.  It  was  then  placed  in  the  sterile  lime 
solution  in  the  sterile  flask  and  allowed  to  remain  5  days.  The 
hair  was  partially  destroyed  and  slipped  easily,  except  in  certain 
spots.  These  spots  were  very  difficult  to  unhair  for  some  reason. 
The  grain  of  this  leather  cracked  and  scuffed  easily  and  was  not 
satisfactory. 

EXPERIMENT  45. 

The  flask  used  in  Experiment  44  containing  the  same  lime  and 
arsenic  sulphide  solution,  was  autoclaved  4  to  5  hours  at  110°  to 
120°  C.,  to  insure  sterility  of  the  contents.  One-half  of  a  dry- 
salted  calfskin  which  had  been  sterilized  for  24  hours  in  a  Sey- 
mour-Jones solution,  was  added  to  the  cooled  flask  with  sterile 
forceps.  This  skin  was  limed  6  days.  Sub-cultures  made  pre- 
cisely as  in  previous  experiments  showed  negative  results  and  that 
the  limes  had  been  sterile.  The  skin  unhaired  easily  except  in  one 
place  an  area  of  about  6  square  inches.  The  white  hair  on  this 
spot  adhered  with  remarkable  tenacity  while  the  black  hair  on 
the  rest  of  the  skin  slipped  easily.  No  explanation  of  this  peculiar 
occurrence  could  be  suggested  at  the  tannery.  The  hide  felt 
"full"  and  the  final  product  was  of  fair  quality.  The  leather  had 
average  tensile  strength  and  a  good  grain  although  it  did  not 
feel  as  full  as  the  standard  product  of  the  tannery.  Stretching 
did  not  crack  the  grain  of  the  final  product  except  on  the  extreme 
flank. 

EXPERIMENT  46. 

To  the  same  lime  solution  in  the  flask  of  Experiment  45  9 
grams  of  red  arsenic  sulphide,  300  grams  of  slaked  lime  and 


60  A   STUDY   OF   THE)    CHANGES   IN    SKINS 

enough  water  were  added  to  bring  the  contents  up  to  the  original 
volume.  This  flask  was  again  autoclaved  4  to  5  hours  at  110°  to 
120°  C.  to  insure  sterility  of  the  contents.  The  piece  of  calfskin 
to  be  used  wa's  sterilized  as  before  in  a  Seymour-Jones  solution 
for  24  hours.  The  hair  slipped  easily  after  6  days.  Sub-cultures 
made  from  this  lime  solution,  on  various  media  as  in  previous 
experiments,  showed  negative  results  and  proved  the  solution  to 
have  been  sterile.  The  final  leather  felt  quite  "full"  in  the  judg- 
ment of  the  tannery  superintendent.  It  had  a  good  grain  and  a 
tensile  strength  greater  than  that  of  the  average  skin  limed  in  the 
ordinary  manner.  It  had  a  very  slight  harshness  which  could 
probably  be  overcome  by  modification  of  the  finishing  process. 
The  leather  felt  very  full  both  in  the  flank  and  at  the  backbone. 
The  flank  appeared  to  be  better  than  in  the  ordinary  product. 

CONCLUSIONS. 

The  foregoing  paper  studies  from  three  different  viewpoints 
the  changes  taking  place  in  hides  during  their  conversion  into 
leather  and  particularly  during  the  liming  process.  A  study  is 
made  of  structural  changes  throughout  the  vegetable  and  mineral 
tanning  processes  as  shown  by  the  microscope;  of  gross  changes 
in  volume,  weight  and  density  of  the  skin;  and  of  the  practi- 
cability of  carrying  out  the  depilation  process  in  sterile  solutions. 

Detailed  methods  have  been  worked  out  for  the  satisfactory 
preparation  of  microscopic  sections  both  by  the  colloidin  and 
freezing  methods.  A  study  of  numerous  sections  of  skin  shows 
that  the  structural  changes  occurring  during  depilation  and  tan- 
nage are  so  gradual  that  only  the  broad  outline  can  be  followed. 
The  inter-fibrillar  substance  in  the  bundles  of  connective  tissue 
dissolves  in  the  liming  process  and  the  fiber  bundles  split  up  into 
their  component  fibrils.  The  flank  is  composed  of  larger,  fewer 
and  more  irregular  fiber  bundles  with  larger  interstitial  spaces 
than  the  better  portions  of  the  skin.  This  gives  a  partial  explan- 
ation of  the  poorer  quality  of  flank  leather. 

When  dry  calfskins  are  put  into  water  they  increase  in  super- 
ficial area,  thickness  and  weight  but  decrease  in  density.  The 
area  remains  almost  constant  during  the  liming  process  in  bacter- 
ial limes,  but  the  volume  and  hence  the  thickness  of  the  skin  in- 
creases quite  consistently  and  at  a  decreasing  rate  during  the 


A   STUDY   OF   THE    CHANGES   IN    SKINS  6 1 

liming  process.  The  weight  increases  at  approximately  the  same 
rate  but  a  study  of  the  relationship  of  weight  and  volume  as 
shown  by  the  density  curves,  indicates  that  the  volume  increases 
faster  than  the  weight  during  the  first  4  or  5  days  in  limes  con- 
taining bacteria  so  that  at  the  end  of  this  period  the  hide  shows 
the  minimum  density  which  it  ever  attains  in  the  limes.  Within 
2  days  after  this  point  is  reached  the  volume  decreases  more 
rapidly  than  the  weight  and  the  density  rises  decidedly.  The  sig- 
nificance of  these  points  of  inflection  of  the  curves  is  not  evident. 

Both  volume  and  weight  decrease  in  the  feebly  acid  bate  used 
but  the  decrease  in  weight  is  greater  than  that  of  the  volume  so 
that  the  density  falls.  In  the  pickle,  conditions  are  the  reverse 
of  those  in  the  bate  and  the  density  rises  sharply.  No  great 
changes  in  weight  volume  or  density  occur  during  the  one  bath 
tannage  used. 

Different  pieces  of  the  same  skin  while  the  same  in  general, 
show  decided  quantitative  variations  from  each  other.  The 
shoulder,  back  and  rump  show  distinct  differences  which  are  not 
constant  in  different  skins.  The  flank,  however,  swells  quite  con- 
sistently more  than  the  rest  of  the  skin,  both  in  water  and  in  the 
limes.  These  differences  may  be  due  to  the  varying  thickness  of 
the  skin  or  to  surface  conditions  such  as  fat.  If  the  flesh  side  is 
painted  with  a  soap  solution  before  immersion  in  the  limes  so 
that  an  insoluble  lime  soap  is  precipitated  upon  it,  the  swelling 
is  greatly  increased. 

It  has  been  shown  that  it  is  2Ossible_tQ_depilate  a  skin  or  hide 
under  strictly  sterile  conditions  with  lime  alone  or  with  the  addi- 
tion of  sulphides.  The  same  sterile  lime  solution  can  be  used  to 
depilate  successive  pieces  of  hide.  Calfskin  kept  for  6  months 
in  sterile  milk  of  lime  shows  a  firm  though  rather  glassy  corium. 
A  skin  kept  a  similar  length  of  time  in  sterile  milk  of  lime  con- 
taining arsenic  or  sodium  sulphide,  is  completely  dissolved.  The 
hair  from  the  skins  in  the  latter  solutions  is  also  dissolved  com- 
pletely, while  that  of  the  skin  in  lime  alone,  appears  almost  un- 
changed. 

Pieces  of  cowhide  and  calfskin  unhaired  under  sterile  condi- 
tions have  been  tanned  and  finished  in  commercial  tanneries  using 
vegetable  and  mineral  tanning  agents,  with  fair  results.  It  seems 
entirely  probably  that  with  a  little  more  experience  in  handling 


62  A   STUDY   OF   THE   CHANGES   IN   SKINS 

sterile  limes  a  good  product,  equal  in  all  respects  to  that  produced 
by  the  present  methods  of  liming  could  be  obtained. 

BIBLIOGRAPHY. 

1.  Jettmar,  Handbuch  der  Chromgerbung  (1900). 

2.  Der  Gerber. 

3.  Procter,  The  Principles  of  Leather  Manufacture. 

4.  Procter,  The  Leather  Industries  Laboratory  Book. 

5.  Collegium. 

6.  Bulletin  de  la  Societe  d'encouragement  pour  1'industrie.  Nationale. 

7.  Dinglers  Polytechnische  Journal. 

8.  Hyde,  Diseases  of  the  Skin  (1909). 

9.  JOURNAL  of  the  American  Leather  Chemists  Association. 
10.  Warthin,  Practical  Pathology. 

ir.  Journal  of  the  Society  of  Chemical  Industry. 

12.  English  Patent  Number  2873. 

13.  Villon,  Traite  de  la  Fabrication  des  cuirs. 

14.  Leather  Trades'  Review. 

15.  Bull.  Syndicat.  Gen.  Cuirs  et  Peaux,  p.  416,  Nov.  10,  1908. 


t," 


Makers 

Syracuse,  N.  Y. 
PAT.  JAN.  2 1,1908 


SO, 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


